Ecto.Schema
Defines a schema for a model.
A schema is a struct with associated metadata that is persisted to a repository. Every schema model is also a struct, that means that you work with models just like you would work with structs.
Example
defmodule User do
use Ecto.Schema
schema "users" do
field :name, :string
field :age, :integer, default: 0
has_many :posts, Post
end
end
By default, a schema will generate both a primary key named id
of type :integer
and belongs_to
associations will generate
foreign keys of type :integer
too. Those setting can be configured
below.
Schema attributes
The schema supports some attributes to be set before hand, configuring the defined schema.
Those attributes are:
@primary_key
- configures the schema primary key. It expects a tuple with the primary key name, type and options. Defaults to{:id, :integer, []}
. When set to false, does not define a primary key in the model;@foreign_key_type
- configures the default foreign key type used bybelongs_to
associations. Defaults to:integer
;@timestamps_type
- configures the default timestamps type used bytimestamps
. Defaults toEcto.DateTime
;@derive
- the same as@derive
available inKernel.defstruct/1
as the schema defines a struct behind the scenes;
The advantage of defining configure the schema via those attributes
is that they can be set with a macro to configure application wide
defaults. For example, if you would like to use uuid
's in all of
your application models, you can do:
# Define a module to be used as base
defmodule MyApp.Model do
defmacro __using__(_) do
quote do
use Ecto.Model
@primary_key {:id, :uuid, []}
@foreign_key_type :uuid
end
end
end
# Now use MyApp.Model to define new models
defmodule MyApp.Comment do
use MyApp.Model
schema "comments" do
belongs_to :post, MyApp.Post
end
end
Any models using MyApp.Model
will get the :id
field with type
:uuid
as primary key.
The belongs_to
association on MyApp.Comment
will also define
a :post_id
field with :uuid
type that references the :id
of
the MyApp.Post
model.
Types and casting
When defining the schema, types need to be given. Types are split in two categories, primitive types and custom types.
Primitive types
The primitive types are:
Ecto type | Elixir type | Literal syntax in query |
---|---|---|
: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, ...>> |
:uuid |
16 byte binary |
uuid(binary_or_string) |
{:array, inner_type} |
list |
[value, value, value, ...] |
:decimal |
Decimal |
|
:datetime |
{{year, month, day}, {hour, min, sec}} |
|
:date |
{year, month, day} |
|
:time |
{hour, min, sec} |
Custom types
Sometimes the primitive types in Ecto are too primitive. For example,
:uuid
relies on the underling binary representation instead of
representing itself as a readable string. That's when Ecto.UUID
comes in.
Ecto.UUID
is a custom type. A custom type is a module that
implements the Ecto.Type
behaviour. By default, Ecto provides the
following custom types:
Custom type | Ecto type | Elixir type |
---|---|---|
Ecto.UUID |
:uuid |
"uuid-string" |
Ecto.DateTime |
:datetime |
%Ecto.DateTime{} |
Ecto.Date |
:date |
%Ecto.Date{} |
Ecto.Time |
:time |
%Ecto.Time{} |
Ecto allow developers to provide their own types too. Read the
Ecto.Type
documentation for more information.
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 weather struct with an invalid value
for temp_lo
:
iex> weather = %Weather{temp_lo: "0"}
iex> weather.temp_lo
"0"
However, if you attempt to persist the struct above, an error will be raised since Ecto validates the types when building the query.
Therefore, when working and manipulating external data, it is
recommended the usage of Ecto.Changeset
's that are able to filter
and properly cast external data. In fact, Ecto.Changeset
and custom
types provide a powerful combination to extend Ecto types and queries.
Finally, models 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
.
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 toschema/2
;__schema__(:primary_key)
- Returns the field that is the primary key ornil
if there is none;__schema__(:fields)
- Returns a list of all non-virtual field names;__schema__(:field, field)
- Returns the type of the given non-virtual field;__schema__(:associations)
- Returns a list of all association field names;__schema__(:association, assoc)
- Returns the association reflection of the given assoc;__schema__(:read_after_writes)
- Non-virtual fields that must be read back from the database after every write (insert or update);__schema__(:load, struct \\ __struct__(), fields_or_idx, values)
- Loads a new model struct from a tuple of non-virtual field values starting at the given index or defined by the given fields;
Furthermore, both __struct__
and __changeset__
functions are
defined so structs and changeset functionalities are available.
Summary↑
association(name, association, opts \\ []) | Defines an association |
belongs_to(name, queryable, opts \\ []) | Indicates a one-to-one association with another model |
field(name, type \\ :string, opts \\ []) | Defines a field on the model schema with given name and type |
has_many(name, queryable, opts \\ []) | Indicates a one-to-many association with another model |
has_one(name, queryable, opts \\ []) | Indicates a one-to-one association with another model |
schema(source, list2) | Defines a schema with a source name and field definitions |
timestamps(opts \\ []) | Generates |
Macros
Defines an association.
This macro is used by belongs_to/3
, has_one/3
and has_many/3
to
define associations. However, custom association mechanisms can be provided
by developers and hooked in via this macro.
Read more about custom associations in Ecto.Associations
.
Indicates a one-to-one association with another model.
The current model belongs to zero or one records of the other model. The other
model often has a has_one
or a has_many
field with the reverse association.
You should use belongs_to
in the table that contains the foreign key. Imagine
a company <-> manager relationship. If the company contains the manager_id
in
the underlying database table, we say the company belongs to manager.
In fact, when you invoke this macro, a field with the name of foreign key is automatically defined in the schema for you.
Options
:foreign_key
- Sets the foreign key field name, defaults to the name of the association suffixed by_id
. For example,belongs_to :company
will define foreign key of:company_id
:references
- Sets the key on the other model to be used for the association, defaults to::id
:auto_field
- When false, does not automatically define a:foreign_key
field, implying the user is defining the field manually elsewhere:type
- Sets the type of automtically defined:foreign_key
. Defaults to::integer
and be set per schema via@foreign_key_type
All other options are forwarded to the underlying foreign key definition
and therefore accept the same options as field/3
.
Examples
defmodule Comment do
use Ecto.Model
schema "comments" do
# This automatically defines a post_id field too
belongs_to :post, Post
end
end
# The post can come preloaded on the comment record
[comment] = Repo.all(from(c in Comment, where: c.id == 42, preload: :post))
comment.post #=> %Post{...}
Defines a field on the model schema with given name and type.
Options
:default
- Sets the default value on the schema and the struct:virtual
- When true, the field is not persisted:read_after_writes
- When true, the field is always read back from the repository after inserts and updates
Indicates a one-to-many association with another model.
The current model has zero or more records of the other model. The other
model 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 model, defaults to the underscored name of the current model suffixed by_id
:references
- Sets the key on the current model to be used for the association, defaults to the primary key on the model:through
- If this association must be defined in terms of existing associations. Read below for more information
Examples
defmodule Post do
use Ecto.Model
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{...}, ...]
hasmany/hasone :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.Model
schema "posts" do
has_many :comments, Comment
has_one :permalink, Permalink
has_many :comments_authors, through: [:comments, :author]
end
end
defmodule Comment do
use Ecto.Model
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 expect 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 model Comment
.
This :through
associations will return all authors for all comments
that belongs to that post:
# Get all comments for a given post
post = Repo.get(Post, 42)
authors = Repo.all assoc(post, :comments_authors)
:through
associations are read-only as they are useful to avoid repetition
allowing the developer to easily retrieve data that is often seem together
but stored across different tables.
: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).authors #=> [%Author{...}, ...]
Finally, :through
can be used with multiple associations (not only 2)
and with associations of any kind, including belongs_to
and others
:through
associations. When the :through
association is expected to
return one or no item, 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{...}
Indicates a one-to-one association with another model.
The current model has zero or one records of the other model. The other
model 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 model, defaults to the underscored name of the current model suffixed by_id
:references
- Sets the key on the current model to be used for the association, defaults to the primary key on the model:through
- If this association must be defined in terms of existing associations. Read the section inhas_many/3
for more information
Examples
defmodule Post do
use Ecto.Model
schema "posts" do
has_one :permalink, Permalink
end
end
# The permalink can come preloaded on the post struct
[post] = Repo.all(from(p in Post, where: p.id == 42, preload: :permalink))
post.permalink #=> %Permalink{...}
Defines a schema with a source name and field definitions.
Generates :inserted_at
and :updated_at
timestamp fields.
When using Ecto.Model
, the fields generated by this macro
will automatically be set to the current time when inserting
and updating values in a repository.
Options
:type
- the timestamps type, defaults toEcto.DateTime
. Can also be set via the@timestamps_type
attribute:inserted_at
- the name of the column for insertion times orfalse
:updated_at
- the name of the column for update times orfalse