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A Common DSL for Migrating Databases

Create a Table

create_table("users", func(t) {
  t.Column("email", "string", {})
  t.Column("twitter_handle", "string", {"size": 50})
  t.Column("age", "integer", {"default": 0})
  t.Column("admin", "bool", {"default": false})
  t.Column("company_id", "uuid", {"default_raw": "uuid_generate_v1()"})
  t.Column("bio", "text", {"null": true})
  t.Column("joined_at", "timestamp", {})

create_table("todos", func(t) {
  t.Column("user_id", "integer", {})
  t.Column("title", "string", {"size": 100})
  t.Column("details", "text", {"null": true})
  t.ForeignKey("user_id", {"users": ["id"]}, {"on_delete": "cascade"})

The create_table function will also generate an id column of type integer that will auto-increment. It will also generate two timestamp columns; created_at and updated_at.

Columns all have the same syntax. First is the name of the column. Second is the type of the field. Third is any options you want to set on that column.

"Common" Types:

  • string
  • text
  • timestamp, time, datetime
  • integer
  • bool

Any other type passed it will be be passed straight through to the underlying database. For example for PostgreSQL you could pass jsonband it will be supported, however, SQLite will yell very loudly at you if you do the same thing!

Supported Options:

  • size - The size of the column. For example if you wanted a varchar(50) in Postgres you would do: t.Column("column_name", "string", {"size": 50})
  • null - By default columns are not allowed to be null.
  • default - The default value you want for this column. By default this is null.
  • default_raw - The default value defined as a database function.

Drop a Table


Rename a Table

rename_table("old_table_name", "new_table_name")

Add a Column

add_column("table_name", "column_name", "string", {})

See above for more details on column types and options.

Alter a column

change_column("table_name", "column_name", "string", {})

Rename a Column

rename_column("table_name", "old_column_name", "new_column_name")

Drop a Column

drop_column("table_name", "column_name")

Add an Index

Supported Options:

  • name - This defaults to table_name_column_name_idx
  • unique

Simple Index:

add_index("table_name", "column_name", {})

Multi-Column Index:

add_index("table_name", ["column_1", "column_2"], {})

Unique Index:

add_index("table_name", "column_name", {"unique": true})

Index Names:

add_index("table_name", "column_name", {}) # name => table_name_column_name_idx
add_index("table_name", "column_name", {"name": "custom_index_name"})

Rename an Index

rename_index("table_name", "old_index_name", "new_index_name")

Drop an Index

drop_index("table_name", "index_name")

Add a Foreign Key

add_foreign_key("table_name", "field", {"ref_table_name": ["ref_column"]}, {
    "name": "optional_fk_name",
    "on_delete": "action",
    "on_update": "action",

Supported Options

  • name - This defaults to table_name_ref_table_name_ref_column_name_fk
  • on_delete - CASCADE, SET NULL, ...
  • on_update

Note: on_update and on_delete are not supported on cockroachDB yet.

Drop a Foreign Key

drop_foreign_key("table_name", "fk_name", {"if_exists": true})

Supported Options

  • if_exists - Adds IF EXISTS condition


raw("select * from users;")

All calls to raw must end with a ;!

Execute an External Command

Sometimes during a migration you need to shell out to an external command.

exec("echo hello")