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schema.ex
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defmodule Ecto.Schema do
@moduledoc ~S"""
An Ecto schema maps external data into Elixir structs.
The definition of the schema is possible through two main APIs:
`schema/2` and `embedded_schema/1`.
`schema/2` is typically used to map data from a persisted source,
usually a database table, into Elixir structs and vice-versa. For
this reason, the first argument of `schema/2` is the source (table)
name. Structs defined with `schema/2` also contain a `__meta__` field
with metadata holding the status of the struct, for example, if it
has been built, loaded or deleted.
On the other hand, `embedded_schema/1` is used for defining schemas
that are embedded in other schemas or only exist in-memory. For example,
you can use such schemas to receive data from a command line interface
and validate it, without ever persisting it elsewhere. Such structs
do not contain a `__meta__` field, as they are never persisted.
Besides working as data mappers, `embedded_schema/1` and `schema/2` can
also be used together to decouple how the data is represented in your
applications from the database. Let's see some examples.
## Example
defmodule User do
use Ecto.Schema
schema "users" do
field :name, :string
field :age, :integer, default: 0
field :password, :string, redact: true
has_many :posts, Post
end
end
By default, a schema will automatically generate a primary key which is named
`id` and of type `:integer`. The `field` macro defines a field in the schema
with given name and type. `has_many` associates many posts with the user
schema. Schemas are regular structs and can be created and manipulated directly
using Elixir's struct API:
iex> user = %User{name: "jane"}
iex> %{user | age: 30}
However, most commonly, structs are cast, validated and manipulated with the
`Ecto.Changeset` module.
Note that the name of the database table does not need to correlate to your
module name. For example, if you are working with a legacy database, you can
reference the table name when you define your schema:
defmodule User do
use Ecto.Schema
schema "legacy_users" do
# ... fields ...
end
end
Embedded schemas are defined similarly to source-based schemas. For example,
you can use an embedded schema to represent your UI, mapping and validating
its inputs, and then you convert such embedded schema to other schemas that
are persisted to the database:
defmodule SignUp do
use Ecto.Schema
embedded_schema do
field :name, :string
field :age, :integer
field :email, :string
field :accepts_conditions, :boolean
end
end
defmodule Profile do
use Ecto.Schema
schema "profiles" do
field :name
field :age
belongs_to :account, Account
end
end
defmodule Account do
use Ecto.Schema
schema "accounts" do
field :email
end
end
The `SignUp` schema can be cast and validated with the help of the
`Ecto.Changeset` module, and afterwards, you can copy its data to
the `Profile` and `Account` structs that will be persisted to the
database with the help of `Ecto.Repo`.
## Redacting fields
A field marked with `redact: true` will display a value of `**redacted**`
when inspected in changes inside a `Ecto.Changeset` and be excluded from
inspect on the schema unless the schema module is tagged with
the option `@ecto_derive_inspect_for_redacted_fields false`.
## Schema attributes
Supported attributes for configuring the defined schema. They must
be set after the `use Ecto.Schema` call and before the `schema/2`
definition.
These attributes are:
* `@primary_key` - configures the schema primary key. It expects
a tuple `{field_name, type, options}` with the primary key field
name, type (typically `:id` or `:binary_id`, but can be any type) and
options. It also accepts `false` to disable the generation of a primary
key field. Defaults to `{:id, :id, autogenerate: true}`.
* `@schema_prefix` - configures the schema prefix. Defaults to `nil`,
which generates structs and queries without prefix. When set, the
prefix will be used by every built struct and on queries whenever
the schema is used in a `from` or a `join`. In PostgreSQL, the prefix
is called "SCHEMA" (typically set via Postgres' `search_path`).
In MySQL the prefix points to databases.
* `@schema_context` - configures the schema context. Defaults to `nil`,
which generates structs and queries without context. Context are not used
by the built-in SQL adapters.
* `@foreign_key_type` - configures the default foreign key type
used by `belongs_to` associations. It must be set in the same
module that defines the `belongs_to`. Defaults to `:id`;
* `@timestamps_opts` - configures the default timestamps type
used by `timestamps`. Defaults to `[type: :naive_datetime]`;
* `@derive` - the same as `@derive` available in `Kernel.defstruct/1`
as the schema defines a struct behind the scenes;
* `@field_source_mapper` - a function that receives the current field name
and returns the mapping of this field name in the underlying source.
In other words, it is a mechanism to automatically generate the `:source`
option for the `field` macro. It defaults to `fn x -> x end`, where no
field transformation is done;
The advantage of configuring the schema via those attributes is
that they can be set with a macro to configure application wide
defaults.
For example, if your database does not support autoincrementing
primary keys and requires something like UUID or a RecordID, you
can configure and use `:binary_id` as your primary key type as follows:
# Define a module to be used as base
defmodule MyApp.Schema do
defmacro __using__(_) do
quote do
use Ecto.Schema
@primary_key {:id, :binary_id, autogenerate: true}
@foreign_key_type :binary_id
end
end
end
# Now use MyApp.Schema to define new schemas
defmodule MyApp.Comment do
use MyApp.Schema
schema "comments" do
belongs_to :post, MyApp.Post
end
end
Any schemas using `MyApp.Schema` will get the `:id` field with type
`:binary_id` as the primary key. We explain what the `:binary_id` type
entails in the next section.
The `belongs_to` association on `MyApp.Comment` will also define
a `:post_id` field with `:binary_id` type that references the `:id`
field of the `MyApp.Post` schema.
## Primary keys
Ecto supports two ID types, called `:id` and `:binary_id`, which are
often used as the type for primary keys and associations.
The `:id` type is used when the primary key is an integer while the
`:binary_id` is used for primary keys in particular binary formats,
which may be `Ecto.UUID` for databases like PostgreSQL and MySQL,
or some specific ObjectID or RecordID often imposed by NoSQL databases.
In both cases, both types have their semantics specified by the
underlying adapter/database. If you use the `:id` type with
`:autogenerate`, it means the database will be responsible for
auto-generation of the id. This is often the case for primary keys
in relational databases which are auto-incremented.
There are two ways to define primary keys in Ecto: using the `@primary_key`
module attribute and using `primary_key: true` as option for `field/3` in
your schema definition. They are not mutually exclusive and can be used
together.
Using `@primary_key` should be preferred for single field primary keys and
sharing primary key definitions between multiple schemas using macros.
Setting `@primary_key` also automatically configures the reference types
for `has_one` and `has_many` associations.
Ecto also supports composite primary keys, which is where you need to use
`primary_key: true` for the fields in your schema. This usually goes along
with setting `@primary_key false` to disable generation of additional
primary key fields.
Besides `:id` and `:binary_id`, which are often used by primary
and foreign keys, Ecto provides a huge variety of types to be used
by any field.
## Types and casting
When defining the schema, types need to be given. Types are split
into two categories, primitive types and custom types.
### Primitive types
The primitive types are:
Ecto type | Elixir type | Literal syntax in query
:---------------------- | :---------------------- | :---------------------
`:id` | `integer` | 1, 2, 3
`:binary_id` | `binary` | `<<int, int, int, ...>>`
`:integer` | `integer` | 1, 2, 3
`:float` | `float` | 1.0, 2.0, 3.0
`:boolean` | `boolean` | true, false
`:string` | UTF-8 encoded `string` | "hello"
`:binary` | `binary` | `<<int, int, int, ...>>`
`{:array, inner_type}` | `list` | `[value, value, value, ...]`
`:map` | `map` |
`{:map, inner_type}` | `map` |
`:decimal` | [`Decimal`](https://github.com/ericmj/decimal) |
`:date` | `Date` |
`:time` | `Time` |
`:time_usec` | `Time` |
`:naive_datetime` | `NaiveDateTime` |
`:naive_datetime_usec` | `NaiveDateTime` |
`:utc_datetime` | `DateTime` |
`:utc_datetime_usec` | `DateTime` |
**Notes:**
* When using database migrations provided by "Ecto SQL", you can pass
your Ecto type as the column type. However, note the same Ecto type
may support multiple database types. For example, all of `:varchar`,
`:text`, `:bytea`, etc. translate to Ecto's `:string`. Similarly,
Ecto's `:decimal` can be used for `:numeric` and other database
types. For more information, see [all migration types](https://hexdocs.pm/ecto_sql/Ecto.Migration.html#module-field-types).
* For the `{:array, inner_type}` and `{:map, inner_type}` type,
replace `inner_type` with one of the valid types, such as `:string`.
* For the `:decimal` type, `+Infinity`, `-Infinity`, and `NaN` values
are not supported, even though the `Decimal` library handles them.
To support them, you can create a custom type.
* For calendar types with and without microseconds, the precision is
enforced when persisting to the DB. For example, casting `~T[09:00:00]`
as `:time_usec` will succeed and result in `~T[09:00:00.000000]`, but
persisting a type without microseconds as `:time_usec` will fail.
Similarly, casting `~T[09:00:00.000000]` as `:time` will succeed, but
persisting will not. This is the same behaviour as seen in other types,
where casting has to be done explicitly and is never performed
implicitly when loading from or dumping to the database.
### Custom types
Besides providing primitive types, Ecto allows custom types to be
implemented by developers, allowing Ecto behaviour to be extended.
A custom type is a module that implements one of the `Ecto.Type`
or `Ecto.ParameterizedType` behaviours. By default, Ecto provides
the following custom types:
Custom type | Database type | Elixir type
:---------------------- | :---------------------- | :---------------------
`Ecto.UUID` | `:uuid` (as a binary) | `string()` (as a UUID)
`Ecto.Enum` | `:string` | `atom()`
Finally, schemas can also have virtual fields by passing the
`virtual: true` option. These fields are not persisted to the database
and can optionally not be type checked by declaring type `:any`.
### The datetime types
Four different datetime primitive types are available:
* `naive_datetime` - has a precision of seconds and casts values
to Elixir's `NaiveDateTime` struct which has no timezone information.
* `naive_datetime_usec` - has a default precision of microseconds and
also casts values to `NaiveDateTime` with no timezone information.
* `utc_datetime` - has a precision of seconds and casts values to
Elixir's `DateTime` struct and expects the time zone to be set to UTC.
* `utc_datetime_usec` has a default precision of microseconds and also
casts values to `DateTime` expecting the time zone be set to UTC.
All of those types are represented by the same timestamp/datetime in the
underlying data storage, the difference are in their precision and how the
data is loaded into Elixir.
Having different precisions allows developers to choose a type that will
be compatible with the database and your project's precision requirements.
For example, some older versions of MySQL do not support microseconds in
datetime fields.
When choosing what datetime type to work with, keep in mind that Elixir
functions like `NaiveDateTime.utc_now/0` have a default precision of 6.
Casting a value with a precision greater than 0 to a non-`usec` type will
truncate all microseconds and set the precision to 0.
### The map type
The map type allows developers to store an Elixir map directly
in the database:
# In your migration
create table(:users) do
add :data, :map
end
# In your schema
field :data, :map
# Now in your code
user = Repo.insert! %User{data: %{"foo" => "bar"}}
Keep in mind that we advise the map keys to be strings or integers
instead of atoms. Atoms may be accepted depending on how maps are
serialized but the database will always convert atom keys to strings
due to security reasons.
In order to support maps, different databases may employ different
techniques. For example, PostgreSQL will store those values in jsonb
fields, allowing you to just query parts of it. MSSQL, on
the other hand, does not yet provide a JSON type, so the value will be
stored in a text field.
For maps to work in such databases, Ecto will need a JSON library.
By default Ecto will use [Jason](https://github.com/michalmuskala/jason)
which needs to be added to your deps in `mix.exs`:
{:jason, "~> 1.0"}
You can however configure the adapter to use another library. For example,
if using Postgres:
config :postgrex, :json_library, YourLibraryOfChoice
Or if using MySQL:
config :mariaex, :json_library, YourLibraryOfChoice
If changing the JSON library, remember to recompile the adapter afterwards
by cleaning the current build:
mix deps.clean --build postgrex
### Casting
When directly manipulating the struct, it is the responsibility of
the developer to ensure the field values have the proper type. For
example, you can create a user struct with an invalid value
for `age`:
iex> user = %User{age: "0"}
iex> user.age
"0"
However, if you attempt to persist the struct above, an error will
be raised since Ecto validates the types when sending them to the
adapter/database.
Therefore, when working with and manipulating external data, it is
recommended to use `Ecto.Changeset`'s that are able to filter
and properly cast external data:
changeset = Ecto.Changeset.cast(%User{}, %{"age" => "0"}, [:age])
user = Repo.insert!(changeset)
**You can use Ecto schemas and changesets to cast and validate any kind
of data, regardless if the data will be persisted to an Ecto repository
or not**.
## Reflection
Any schema module will generate the `__schema__` function that can be
used for runtime introspection of the schema:
* `__schema__(:source)` - Returns the source as given to `schema/2`;
* `__schema__(:prefix)` - Returns optional prefix for source provided by
`@schema_prefix` schema attribute;
* `__schema__(:primary_key)` - Returns a list of primary key fields (empty if there is none);
* `__schema__(:fields)` - Returns a list of all non-virtual field names;
* `__schema__(:virtual_fields)` - Returns a list of all virtual field names;
* `__schema__(:field_source, field)` - Returns the alias of the given field;
* `__schema__(:type, field)` - Returns the type of the given non-virtual field;
* `__schema__(:virtual_type, field)` - Returns the type of the given virtual field;
* `__schema__(:associations)` - Returns a list of all association field names;
* `__schema__(:association, assoc)` - Returns the association reflection of the given assoc;
* `__schema__(:embeds)` - Returns a list of all embedded field names;
* `__schema__(:embed, embed)` - Returns the embedding reflection of the given embed;
* `__schema__(:read_after_writes)` - Non-virtual fields that must be read back
from the database after every write (insert or update);
* `__schema__(:autogenerate_id)` - Primary key that is auto generated on insert;
* `__schema__(:redact_fields)` - Returns a list of redacted field names;
Furthermore, both `__struct__` and `__changeset__` functions are
defined so structs and changeset functionalities are available.
## Working with typespecs
Generating typespecs for schemas is out of the scope of `Ecto.Schema`.
In order to be able to use types such as `User.t()`, `t/0` has to be defined manually:
defmodule User do
use Ecto.Schema
@type t :: %__MODULE__{
name: String.t(),
age: non_neg_integer()
}
# ... schema ...
end
Defining the type of each field is not mandatory, but it is preferable.
"""
alias Ecto.Schema.Metadata
@type source :: String.t
@type prefix :: String.t | nil
@type schema :: %{optional(atom) => any, __struct__: atom, __meta__: Metadata.t}
@type embedded_schema :: %{optional(atom) => any, __struct__: atom}
@type t :: schema | embedded_schema
@type belongs_to(t) :: t | Ecto.Association.NotLoaded.t()
@type has_one(t) :: t | Ecto.Association.NotLoaded.t()
@type has_many(t) :: [t] | Ecto.Association.NotLoaded.t()
@type many_to_many(t) :: [t] | Ecto.Association.NotLoaded.t()
@type embeds_one(t) :: t
@type embeds_many(t) :: [t]
@doc false
defmacro __using__(_) do
quote do
import Ecto.Schema, only: [schema: 2, embedded_schema: 1]
@primary_key nil
@timestamps_opts []
@foreign_key_type :id
@schema_prefix nil
@schema_context nil
@field_source_mapper fn x -> x end
Module.register_attribute(__MODULE__, :ecto_primary_keys, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_fields, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_virtual_fields, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_query_fields, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_field_sources, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_assocs, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_embeds, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_raw, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_autogenerate, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_autoupdate, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_redact_fields, accumulate: true)
Module.put_attribute(__MODULE__, :ecto_derive_inspect_for_redacted_fields, true)
Module.put_attribute(__MODULE__, :ecto_autogenerate_id, nil)
end
end
@field_opts [
:default,
:source,
:autogenerate,
:read_after_writes,
:virtual,
:primary_key,
:load_in_query,
:redact,
:foreign_key,
:on_replace,
:defaults,
:type,
:where,
:references,
:skip_default_validation
]
@doc """
Defines an embedded schema with the given field definitions.
An embedded schema is either embedded into another
schema or kept exclusively in memory. For this reason,
an embedded schema does not require a source name and
it does not include a metadata field.
Embedded schemas by default set the primary key type
to `:binary_id` but such can be configured with the
`@primary_key` attribute.
"""
defmacro embedded_schema([do: block]) do
schema(__CALLER__, nil, false, :binary_id, block)
end
@doc """
Defines a schema struct with a source name and field definitions.
An additional field called `__meta__` is added to the struct for storing
internal Ecto state. This field always has a `Ecto.Schema.Metadata` struct
as value and can be manipulated with the `Ecto.put_meta/2` function.
"""
defmacro schema(source, [do: block]) do
schema(__CALLER__, source, true, :id, block)
end
defp schema(caller, source, meta?, type, block) do
prelude =
quote do
if line = Module.get_attribute(__MODULE__, :ecto_schema_defined) do
raise "schema already defined for #{inspect(__MODULE__)} on line #{line}"
end
@ecto_schema_defined unquote(caller.line)
@after_compile Ecto.Schema
Module.register_attribute(__MODULE__, :ecto_changeset_fields, accumulate: true)
Module.register_attribute(__MODULE__, :ecto_struct_fields, accumulate: true)
meta? = unquote(meta?)
source = unquote(source)
prefix = @schema_prefix
context = @schema_context
# Those module attributes are accessed only dynamically
# so we explicitly reference them here to avoid warnings.
_ = @foreign_key_type
_ = @timestamps_opts
if meta? do
unless is_binary(source) do
raise ArgumentError, "schema source must be a string, got: #{inspect source}"
end
meta = %Metadata{
state: :built,
source: source,
prefix: prefix,
context: context,
schema: __MODULE__
}
Module.put_attribute(__MODULE__, :ecto_struct_fields, {:__meta__, meta})
end
if @primary_key == nil do
@primary_key {:id, unquote(type), autogenerate: true}
end
primary_key_fields =
case @primary_key do
false ->
[]
{name, type, opts} ->
Ecto.Schema.__field__(__MODULE__, name, type, [primary_key: true] ++ opts)
[name]
other ->
raise ArgumentError, "@primary_key must be false or {name, type, opts}"
end
try do
import Ecto.Schema
unquote(block)
after
:ok
end
end
postlude =
quote unquote: false do
primary_key_fields = @ecto_primary_keys |> Enum.reverse
autogenerate = @ecto_autogenerate |> Enum.reverse
autoupdate = @ecto_autoupdate |> Enum.reverse
fields = @ecto_fields |> Enum.reverse
query_fields = @ecto_query_fields |> Enum.reverse
virtual_fields = @ecto_virtual_fields |> Enum.reverse
field_sources = @ecto_field_sources |> Enum.reverse
assocs = @ecto_assocs |> Enum.reverse
embeds = @ecto_embeds |> Enum.reverse
redacted_fields = @ecto_redact_fields
loaded = Ecto.Schema.__loaded__(__MODULE__, @ecto_struct_fields)
if redacted_fields != [] and not List.keymember?(@derive, Inspect, 0) and
@ecto_derive_inspect_for_redacted_fields do
@derive {Inspect, except: @ecto_redact_fields}
end
defstruct Enum.reverse(@ecto_struct_fields)
def __changeset__ do
%{unquote_splicing(Macro.escape(@ecto_changeset_fields))}
end
def __schema__(:prefix), do: unquote(prefix)
def __schema__(:source), do: unquote(source)
def __schema__(:fields), do: unquote(Enum.map(fields, &elem(&1, 0)))
def __schema__(:query_fields), do: unquote(Enum.map(query_fields, &elem(&1, 0)))
def __schema__(:primary_key), do: unquote(primary_key_fields)
def __schema__(:hash), do: unquote(:erlang.phash2({primary_key_fields, query_fields}))
def __schema__(:read_after_writes), do: unquote(Enum.reverse(@ecto_raw))
def __schema__(:autogenerate_id), do: unquote(Macro.escape(@ecto_autogenerate_id))
def __schema__(:autogenerate), do: unquote(Macro.escape(autogenerate))
def __schema__(:autoupdate), do: unquote(Macro.escape(autoupdate))
def __schema__(:loaded), do: unquote(Macro.escape(loaded))
def __schema__(:redact_fields), do: unquote(redacted_fields)
def __schema__(:virtual_fields), do: unquote(Enum.map(virtual_fields, &elem(&1, 0)))
def __schema__(:query) do
%Ecto.Query{
from: %Ecto.Query.FromExpr{
source: {unquote(source), __MODULE__},
prefix: unquote(prefix)
}
}
end
for clauses <- Ecto.Schema.__schema__(fields, field_sources, assocs, embeds, virtual_fields),
{args, body} <- clauses do
def __schema__(unquote_splicing(args)), do: unquote(body)
end
end
quote do
unquote(prelude)
unquote(postlude)
end
end
## API
@doc """
Defines a field on the schema with given name and type.
The field name will be used as is to read and write to the database
by all of the built-in adapters unless overridden with the `:source`
option.
## Options
* `:default` - Sets the default value on the schema and the struct.
The default value is calculated at compilation time, so don't use
expressions like `DateTime.utc_now` or `Ecto.UUID.generate` as
they would then be the same for all records: in this scenario you can use
the `:autogenerate` option to generate at insertion time.
The default value is validated against the field's type at compilation time
and it will raise an ArgumentError if there is a type mismatch. If you cannot
infer the field's type at compilation time, you can use the
`:skip_default_validation` option on the field to skip validations.
Once a default value is set, if you send changes to the changeset that
contains the same value defined as default, validations will not be performed
since there are no changes after all.
* `:source` - Defines the name that is to be used in database for this field.
This is useful when attaching to an existing database. The value should be
an atom.
* `:autogenerate` - a `{module, function, args}` tuple for a function
to call to generate the field value before insertion if value is not set.
A shorthand value of `true` is equivalent to `{type, :autogenerate, []}`.
* `:read_after_writes` - When true, the field is always read back
from the database after insert and updates.
For relational databases, this means the RETURNING option of those
statements is used. For this reason, MySQL does not support this
option and will raise an error if a schema is inserted/updated with
read after writes fields.
* `:virtual` - When true, the field is not persisted to the database.
Notice virtual fields do not support `:autogenerate` nor
`:read_after_writes`.
* `:primary_key` - When true, the field is used as part of the
composite primary key.
* `:load_in_query` - When false, the field will not be loaded when
selecting the whole struct in a query, such as `from p in Post, select: p`.
Defaults to `true`.
* `:redact` - When true, it will display a value of `**redacted**`
when inspected in changes inside a `Ecto.Changeset` and be excluded
from inspect on the schema. Defaults to `false`.
* `:skip_default_validation` - When true, it will skip the type validation
step at compile time.
"""
defmacro field(name, type \\ :string, opts \\ []) do
quote do
Ecto.Schema.__field__(__MODULE__, unquote(name), unquote(type), unquote(opts))
end
end
@doc """
Generates `:inserted_at` and `:updated_at` timestamp fields.
The fields generated by this macro will automatically be set to
the current time when inserting and updating values in a repository.
## Options
* `:inserted_at` - the Ecto schema name of the field for insertion times or `false`
* `:updated_at` - the Ecto schema name of the field for update times or `false`
* `:inserted_at_source` - the name of the database column for insertion times or `false`
* `:updated_at_source` - the name of the database column for update times or `false`
* `:type` - the timestamps type, defaults to `:naive_datetime`.
* `:autogenerate` - a module-function-args tuple used for generating
both `inserted_at` and `updated_at` timestamps
All options can be pre-configured by setting `@timestamps_opts`.
"""
defmacro timestamps(opts \\ []) do
quote bind_quoted: binding() do
timestamps = Keyword.merge(@timestamps_opts, opts)
type = Keyword.get(timestamps, :type, :naive_datetime)
autogen = timestamps[:autogenerate] || {Ecto.Schema, :__timestamps__, [type]}
inserted_at = Keyword.get(timestamps, :inserted_at, :inserted_at)
updated_at = Keyword.get(timestamps, :updated_at, :updated_at)
if inserted_at do
opts = if source = timestamps[:inserted_at_source], do: [source: source], else: []
Ecto.Schema.field(inserted_at, type, opts)
end
if updated_at do
opts = if source = timestamps[:updated_at_source], do: [source: source], else: []
Ecto.Schema.field(updated_at, type, opts)
Module.put_attribute(__MODULE__, :ecto_autoupdate, {[updated_at], autogen})
end
with [_ | _] = fields <- Enum.filter([inserted_at, updated_at], & &1) do
Module.put_attribute(__MODULE__, :ecto_autogenerate, {fields, autogen})
end
:ok
end
end
@doc ~S"""
Indicates a one-to-many association with another schema.
The current schema has zero or more records of the other schema. The other
schema often has a `belongs_to` field with the reverse association.
## Options
* `:foreign_key` - Sets the foreign key, this should map to a field on the
other schema, defaults to the underscored name of the current schema
suffixed by `_id`
* `:references` - Sets the key on the current schema to be used for the
association, defaults to the primary key on the schema
* `:through` - Allow this association to be defined in terms of existing
associations. Read the section on `:through` associations for more info
* `:on_delete` - The action taken on associations when parent record
is deleted. May be `:nothing` (default), `:nilify_all` and `:delete_all`.
Using this option is DISCOURAGED for most relational databases. Instead,
in your migration, set `references(:parent_id, on_delete: :delete_all)`.
Opposite to the migration option, this option cannot guarantee integrity
and it is only triggered for `c:Ecto.Repo.delete/2` (and not on
`c:Ecto.Repo.delete_all/2`) and it never cascades. If posts has many comments,
which has many tags, and you delete a post, only comments will be deleted.
If your database does not support references, cascading can be manually
implemented by using `Ecto.Multi` or `Ecto.Changeset.prepare_changes/2`.
* `:on_replace` - The action taken on associations when the record is
replaced when casting or manipulating parent changeset. May be
`:raise` (default), `:mark_as_invalid`, `:nilify`, `:delete` or
`:delete_if_exists`. See `Ecto.Changeset`'s section about `:on_replace` for
more info.
* `:defaults` - Default values to use when building the association.
It may be a keyword list of options that override the association schema
or a atom/`{module, function, args}` that receives the struct and the owner as
arguments. For example, if you set `Post.has_many :comments, defaults: [public: true]`,
then when using `Ecto.build_assoc(post, :comments)`, the comment will have
`comment.public == true`. Alternatively, you can set it to
`Post.has_many :comments, defaults: :update_comment`, which will invoke
`Post.update_comment(comment, post)`, or set it to a MFA tuple such as
`{Mod, fun, [arg3, arg4]}`, which will invoke `Mod.fun(comment, post, arg3, arg4)`
* `:where` - A filter for the association. See "Filtering associations" below.
It does not apply to `:through` associations.
* `:preload_order` - Sets the default `order_by` of the association.
It is used when the association is preloaded.
For example, if you set `Post.has_many :comments, preload_order: [asc: :content]`,
whenever the `:comments` associations is preloaded,
the comments will be order by the `:content` field.
See `Ecto.Query.order_by/3` for more examples.
## Examples
defmodule Post do
use Ecto.Schema
schema "posts" do
has_many :comments, Comment
end
end
# Get all comments for a given post
post = Repo.get(Post, 42)
comments = Repo.all assoc(post, :comments)
# The comments can come preloaded on the post struct
[post] = Repo.all(from(p in Post, where: p.id == 42, preload: :comments))
post.comments #=> [%Comment{...}, ...]
`has_many` can be used to define hierarchical relationships within a single
schema, for example threaded comments.
defmodule Comment do
use Ecto.Schema
schema "comments" do
field :content, :string
field :parent_id, :integer
belongs_to :parent, Comment, foreign_key: :parent_id, references: :id, define_field: false
has_many :children, Comment, foreign_key: :parent_id, references: :id
end
end
## Filtering associations
It is possible to specify a `:where` option that will filter the records
returned by the association. Querying, joining or preloading the association
will use the given conditions as shown next:
defmodule Post do
use Ecto.Schema
schema "posts" do
has_many :public_comments, Comment,
where: [public: true]
end
end
The `:where` option expects a keyword list where the key is an atom
representing the field and the value is either:
* `nil` - which specifies the field must be nil
* `{:not, nil}` - which specifies the field must not be nil
* `{:in, list}` - which specifies the field must be one of the values in a list
* `{:fragment, expr}` - which specifies a fragment string as the filter
(see `Ecto.Query.API.fragment/1`) with the field's value given to it
as the only argument
* or any other value which the field is compared directly against
Note the values above are distinctly different from the values you
would pass to `where` when building a query. For example, if you
attempt to build a query such as
from Post, where: [id: nil]
it will emit an error. This is because queries can be built dynamically,
and therefore passing `nil` can lead to security errors. However, the
`:where` values for an association are given at compile-time, which is
less dynamic and cannot leverage the full power of Ecto queries, which
explains why they have different APIs.
**Important!** Please use this feature only when strictly necessary,
otherwise it is very easy to end-up with large schemas with dozens of
different associations polluting your schema and affecting your
application performance. For instance, if you are using associations
only for different querying purposes, then it is preferable to build
and compose queries. For instance, instead of having two associations,
one for comments and another for deleted comments, you might have
a single comments association and filter it instead:
posts
|> Ecto.assoc(:comments)
|> Comment.deleted()
Or when preloading:
from posts, preload: [comments: ^Comment.deleted()]
## has_many/has_one :through
Ecto also supports defining associations in terms of other associations
via the `:through` option. Let's see an example:
defmodule Post do
use Ecto.Schema
schema "posts" do
has_many :comments, Comment
has_one :permalink, Permalink
# In the has_many :through example below, the `:comments`
# in the list [:comments, :author] refers to the
# `has_many :comments` in the Post own schema and the
# `:author` refers to the `belongs_to :author` of the
# Comment's schema (the module below).
# (see the description below for more details)
has_many :comments_authors, through: [:comments, :author]
# Specify the association with custom source
has_many :tags, {"posts_tags", Tag}
end
end
defmodule Comment do
use Ecto.Schema
schema "comments" do
belongs_to :author, Author
belongs_to :post, Post
has_one :post_permalink, through: [:post, :permalink]
end
end
In the example above, we have defined a `has_many :through` association
named `:comments_authors`. A `:through` association always expects a list
and the first element of the list must be a previously defined association
in the current module. For example, `:comments_authors` first points to
`:comments` in the same module (Post), which then points to `:author` in
the next schema, `Comment`.
This `:through` association will return all authors for all comments
that belongs to that post:
# Get all comments authors for a given post
post = Repo.get(Post, 42)
authors = Repo.all assoc(post, :comments_authors)
`:through` associations can also be preloaded. In such cases, not only
the `:through` association is preloaded but all intermediate steps are
preloaded too:
[post] = Repo.all(from(p in Post, where: p.id == 42, preload: :comments_authors))
post.comments_authors #=> [%Author{...}, ...]
# The comments for each post will be preloaded too
post.comments #=> [%Comment{...}, ...]
# And the author for each comment too
hd(post.comments).author #=> %Author{...}
When the `:through` association is expected to return one or zero items,
`has_one :through` should be used instead, as in the example at the beginning
of this section:
# How we defined the association above
has_one :post_permalink, through: [:post, :permalink]
# Get a preloaded comment
[comment] = Repo.all(Comment) |> Repo.preload(:post_permalink)
comment.post_permalink #=> %Permalink{...}
Note `:through` associations are read-only. For example, you cannot use
`Ecto.Changeset.cast_assoc/3` to modify through associations.
"""
defmacro has_many(name, queryable, opts \\ []) do
queryable = expand_alias(queryable, __CALLER__)
quote do
Ecto.Schema.__has_many__(__MODULE__, unquote(name), unquote(queryable), unquote(opts))
end
end
@doc ~S"""
Indicates a one-to-one association with another schema.
The current schema has zero or one records of the other schema. The other
schema often has a `belongs_to` field with the reverse association.