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query_methods.cr
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query_methods.cr
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module DB
# Methods to allow querying a database.
# All methods accepts a `query : String` and a set arguments.
#
# Three kind of statements can be performed:
# 1. `#exec` waits no record response from the database. An `ExecResult` is returned.
# 2. `#scalar` reads a single value of the response. A union of possible values is returned.
# 3. `#query` returns a `ResultSet` that allows iteration over the rows in the response and column information.
#
# Arguments can be passed by position
#
# ```
# db.query("SELECT name FROM ... WHERE age > ?", age)
# ```
#
# Convention of mapping how arguments are mapped to the query depends on each driver.
#
# Including `QueryMethods` requires a `build(query) : Statement` method that is not expected
# to be called directly.
module QueryMethods(Stmt)
# :nodoc:
abstract def build(query) : Stmt
# Executes a *query* and returns a `ResultSet` with the results.
# The `ResultSet` must be closed manually.
#
# ```
# result = db.query "select name from contacts where id = ?", 10
# begin
# if result.move_next
# id = result.read(Int32)
# end
# ensure
# result.close
# end
# ```
def query(query, *args)
build(query).query(*args)
end
# Executes a *query* and yields a `ResultSet` with the results.
# The `ResultSet` is closed automatically.
#
# ```
# db.query("select name from contacts where age > ?", 18) do |rs|
# rs.each do
# name = rs.read(String)
# end
# end
# ```
def query(query, *args)
# CHECK build(query).query(*args, &block)
rs = query(query, *args)
yield rs ensure rs.close
end
# Executes a *query* that expects a single row and yields a `ResultSet`
# positioned at that first row.
#
# The given block must not invoke `move_next` on the yielded result set.
#
# Raises `DB::Error` if there were no rows, or if there were more than one row.
#
# ```
# name = db.query_one "select name from contacts where id = ?", 18, &.read(String)
# ```
def query_one(query, *args, &block : ResultSet -> U) : U forall U
query(query, *args) do |rs|
raise DB::Error.new("no rows") unless rs.move_next
value = yield rs
raise DB::Error.new("more than one row") if rs.move_next
return value
end
end
# Executes a *query* that expects a single row and returns it
# as a tuple of the given *types*.
#
# Raises `DB::Error` if there were no rows, or if there were more than one row.
#
# ```
# db.query_one "select name, age from contacts where id = ?", 1, as: {String, Int32}
# ```
def query_one(query, *args, as types : Tuple)
query_one(query, *args) do |rs|
rs.read(*types)
end
end
# Executes a *query* that expects a single row and returns it
# as a named tuple of the given *types* (the keys of the named tuple
# are not necessarily the column names).
#
# Raises `DB::Error` if there were no rows, or if there were more than one row.
#
# ```
# db.query_one "select name, age from contacts where id = ?", 1, as: {name: String, age: Int32}
# ```
def query_one(query, *args, as types : NamedTuple)
query_one(query, *args) do |rs|
rs.read(**types)
end
end
# Executes a *query* that expects a single row
# and returns the first column's value as the given *type*.
#
# Raises `DB::Error` if there were no rows, or if there were more than one row.
#
# ```
# db.query_one "select name from contacts where id = ?", 1, as: String
# ```
def query_one(query, *args, as type : Class)
query_one(query, *args) do |rs|
rs.read(type)
end
end
# Executes a *query* that expects at most a single row and yields a `ResultSet`
# positioned at that first row.
#
# Returns `nil`, not invoking the block, if there were no rows.
#
# Raises `DB::Error` if there were more than one row
# (this ends up invoking the block once).
#
# ```
# name = db.query_one? "select name from contacts where id = ?", 18, &.read(String)
# typeof(name) # => String | Nil
# ```
def query_one?(query, *args, &block : ResultSet -> U) : U? forall U
query(query, *args) do |rs|
return nil unless rs.move_next
value = yield rs
raise DB::Error.new("more than one row") if rs.move_next
return value
end
end
# Executes a *query* that expects a single row and returns it
# as a tuple of the given *types*.
#
# Returns `nil` if there were no rows.
#
# Raises `DB::Error` if there were more than one row.
#
# ```
# result = db.query_one? "select name, age from contacts where id = ?", 1, as: {String, Int32}
# typeof(result) # => Tuple(String, Int32) | Nil
# ```
def query_one?(query, *args, as types : Tuple)
query_one?(query, *args) do |rs|
rs.read(*types)
end
end
# Executes a *query* that expects a single row and returns it
# as a named tuple of the given *types* (the keys of the named tuple
# are not necessarily the column names).
#
# Returns `nil` if there were no rows.
#
# Raises `DB::Error` if there were more than one row.
#
# ```
# result = db.query_one? "select name, age from contacts where id = ?", 1, as: {age: String, name: Int32}
# typeof(result) # => NamedTuple(age: String, name: Int32) | Nil
# ```
def query_one?(query, *args, as types : NamedTuple)
query_one?(query, *args) do |rs|
rs.read(**types)
end
end
# Executes a *query* that expects a single row
# and returns the first column's value as the given *type*.
#
# Returns `nil` if there were no rows.
#
# Raises `DB::Error` if there were more than one row.
#
# ```
# name = db.query_one? "select name from contacts where id = ?", 1, as: String
# typeof(name) # => String?
# ```
def query_one?(query, *args, as type : Class)
query_one?(query, *args) do |rs|
rs.read(type)
end
end
# Executes a *query* and yield a `ResultSet` positioned at the beginning
# of each row, returning an array of the values of the blocks.
#
# ```
# names = db.query_all "select name from contacts", &.read(String)
# ```
def query_all(query, *args, &block : ResultSet -> U) : Array(U) forall U
ary = [] of U
query_each(query, *args) do |rs|
ary.push(yield rs)
end
ary
end
# Executes a *query* and returns an array where each row is
# read as a tuple of the given *types*.
#
# ```
# contacts = db.query_all "select name, age from contacts", as: {String, Int32}
# ```
def query_all(query, *args, as types : Tuple)
query_all(query, *args) do |rs|
rs.read(*types)
end
end
# Executes a *query* and returns an array where each row is
# read as a named tuple of the given *types* (the keys of the named tuple
# are not necessarily the column names).
#
# ```
# contacts = db.query_all "select name, age from contacts", as: {name: String, age: Int32}
# ```
def query_all(query, *args, as types : NamedTuple)
query_all(query, *args) do |rs|
rs.read(**types)
end
end
# Executes a *query* and returns an array where the
# value of each row is read as the given *type*.
#
# ```
# names = db.query_all "select name from contacts", as: String
# ```
def query_all(query, *args, as type : Class)
query_all(query, *args) do |rs|
rs.read(type)
end
end
# Executes a *query* and yields the `ResultSet` once per each row.
# The `ResultSet` is closed automatically.
#
# ```
# db.query_each "select name from contacts" do |rs|
# puts rs.read(String)
# end
# ```
def query_each(query, *args)
query(query, *args) do |rs|
rs.each do
yield rs
end
end
end
# Performs the `query` and returns an `ExecResult`
def exec(query, *args)
build(query).exec(*args)
end
# Performs the `query` and returns a single scalar value
#
# ```
# puts db.scalar("SELECT MAX(name)").as(String) # => (a String)
# ```
def scalar(query, *args)
build(query).scalar(*args)
end
end
end