Querying the Database

The Query class provides building robust composable query builder for retrieving and manipulate data.

Generally (but not necessary), its easiest to define a shortcut variable at the top level of your application.

Query = Crecto::Repo::Query

The query object can be composed and manipulated before being used.

query = Query.new
query = query.where(is_admin: true) if role === "admin"
query = query.where(is_user: true) if role === "user"
Repo.all(User, query)

Query methods

where

Query.where(name: "Aaliyah").where(is_admin: false)

or_where

Query.where(role: "admin").or_where(role: "user")

select

Query.select(["id", "name"])

limit

Query.where(name: "Usher").limit(10)

offset

Query.where(name: "Aretha").limit(10).offset(10)

order_by

Query.order_by("created_at DESC")

join

# SELECT * FROM users INNER JOIN images ON images.user_id = users.id
# WHERE images.file_name = ?
class User
  # schema ...
  has_many :images
end

class Image
  schema "images" do
    field :file_name
  end

  belogns_to :user
end
query = Query.join(:images).where("images.file_name = ?", "crystal.jpg")
Repo.all(User, query)

distinct

Query.distinct("users.name")

group_by

Query.where(name: "Charlize").join(:posts).group_by("users.id")

preload

Query.preload(:images)

Nested grouped queries

and

With a block:

query = Query.where(foo: "bar").and do |q|
  q.where(name: "GZA").or_where(name: "RZA")
end

With multiple query objects:

query = Query.where(foo: "bar").and(
  Query.where(name: "GZA").or_where(name: "RZA")
)

Would both produce the same query from Repo.all(User, query):

SELECT users.* FROM users WHERE ((users.foo='bar') AND ((users.name='GZA') OR (users.name='RZA')))

or

With a block:

query = Query.where(foo: "bar").or do |q|
  q.where(foo: "baz").where(name: "ODB")
end

With multiple query objects:

query = Query.where(foo: "bar").or(
  Query.where(foo: "baz").where(name: "ODB")
)

Would both produce the same query from Repo.all(User, query):

SELECT users.* FROM users WHERE ((users.foo='bar') OR ((users.foo='baz') AND (users.name='ODB')))