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A toolkit for data mapping and language integrated query for Elixir
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Files
lib/ecto/migration.ex
defmodule Ecto.Migration do
@moduledoc """
Migrations are used to modify your database schema over time.
This module provides many helpers for migrating the database,
allowing developers to use Elixir to alter their storage in
a way it is database independent.
Here is an example:
defmodule MyRepo.Migrations.CreatePosts do
use Ecto.Migration
def up do
create table(:weather) do
add :city, :string, size: 40
add :temp_lo, :integer
add :temp_hi, :integer
add :prcp, :float
timestamps
end
end
def down do
drop table(:weather)
end
end
Note migrations have an `up/0` and `down/0` instructions, where
`up/0` is used to update your database and `down/0` rolls back
the prompted changes.
Ecto provides some mix tasks to help developers work with migrations:
* `mix ecto.gen.migration add_weather_table` - generates a
migration that the user can fill in with particular commands
* `mix ecto.migrate` - migrates a repository
* `mix ecto.rollback` - rolls back a particular migration
Run the `mix help COMMAND` for more information.
## Change
Migrations can also be automatically reversible by implementing
`change/0` instead of `up/0` and `down/0`. For example, the
migration above can be written as:
defmodule MyRepo.Migrations.CreatePosts do
use Ecto.Migration
def change do
create table(:weather) do
add :city, :string, size: 40
add :temp_lo, :integer
add :temp_hi, :integer
add :prcp, :float
timestamps
end
end
end
Notice not all commands are reversible though. Trying to rollback
a non-reversible command will raise an `Ecto.MigrationError`.
"""
defmodule Index do
@moduledoc """
Defines an index struct used in migrations.
"""
defstruct table: nil, name: nil, columns: [], unique: false
@type t :: %__MODULE__{table: atom, name: atom, columns: [atom | String.t], unique: boolean}
end
defmodule Table do
@moduledoc """
Defines a table struct used in migrations.
"""
defstruct name: nil, primary_key: true
@type t :: %__MODULE__{name: atom, primary_key: boolean}
end
defmodule Reference do
@moduledoc """
Defines a reference struct used in migrations.
"""
defstruct table: nil, column: :id, type: :integer
@type t :: %__MODULE__{table: atom, column: atom, type: atom}
end
alias Ecto.Migration.Runner
@doc false
defmacro __using__(_) do
quote location: :keep do
import Ecto.Migration
def __migration__, do: true
end
end
@doc """
Creates a table.
By default, the table will also include a primary_key of name `:id`
and type `:serial`. Check `table/2` docs for more information.
## Examples
create table(:posts) do
add :title, :string, default: "Untitled"
add :body, :text
timestamps
end
"""
defmacro create(object, do: block) do
quote do
table = unquote(object)
Runner.start_command({:create, table})
if table.primary_key do
add(:id, :serial, primary_key: true)
end
unquote(block)
Runner.end_command
end
end
@doc """
Alters a table.
## Examples
alter table(:posts) do
add :summary, :text
modify :title, :text
remove :views
end
"""
defmacro alter(object, do: block) do
quote do
Runner.start_command({:alter, unquote(object)})
unquote(block)
Runner.end_command
end
end
@doc """
Creates an index.
## Examples
create index(:posts, [:name])
"""
def create(%{} = object) do
Runner.execute {:create, object}
end
@doc """
Drops a table or index.
## Examples
drop index(:posts, [:name])
drop table(:posts)
"""
def drop(%{} = object) do
Runner.execute {:drop, object}
end
@doc """
Returns a table struct that can be given on create, alter, etc.
## Examples
create table(:products) do
add :name, :string
add :price, :decimal
end
drop table(:products)
create table(:products, primary_key: false) do
add :name, :string
add :price, :decimal
end
## Options
* `:primary_key` - when false, does not generate primary key on table creation
"""
def table(name, opts \\ []) when is_atom(name) do
struct(%Table{name: name}, opts)
end
@doc """
Returns an index struct that can be used on `create`, `drop`, etc.
Expects the table name as first argument and the index fields as
second. The field can be an atom, representing a column, or a
string representing an expression that is sent as is to the database.
Indexes are non-unique by default.
## Examples
# Without a name, index defaults to products_category_id_sku_index
create index(:products, [:category_id, :sku], unique: true)
# Name can be given explicitly though
drop index(:products, [:category_id, :sku], name: :my_special_name)
"""
def index(table, columns, opts \\ []) when is_atom(table) and is_list(columns) do
index = struct(%Index{table: table, columns: columns}, opts)
%{index | name: index.name || default_index_name(index)}
end
defp default_index_name(index) do
[index.table, index.columns, "index"]
|> List.flatten
|> Enum.join("_")
|> String.replace(~r"[^\w_]", "_")
|> String.replace("__", "_")
|> String.to_atom
end
@doc """
Executes arbitrary SQL.
## Examples
execute "UPDATE posts SET published_at = NULL"
"""
def execute(command) when is_binary(command) do
Runner.execute command
end
@doc """
Adds a column when creating or altering a table.
## Examples
create table(:posts) do
add :title, :string, default: "Untitled"
end
alter table(:posts) do
add :summary, :text
end
## Options
* `:default` - the column's default value.
* `:primary_key` - when true, marks this field as the primary key
* `:null` - when `false`, the column does not allow null values.
* `:size` - the size of the type (for example the numbers of characters). Default is no size.
* `:precision` - the precision for a numberic type. Default is no precision.
* `:scale` - the scale of a numberic type. Default is 0 scale.
"""
def add(column, type \\ :string, opts \\ []) when is_atom(column) do
Runner.subcommand {:add, column, type, opts}
end
@doc """
Adds `:inserted_at` and `:updated_at` timestamps columns.
Those columns are of `:datetime` type and cannot be null.
"""
def timestamps do
add(:inserted_at, :datetime, null: false)
add(:updated_at, :datetime, null: false)
end
@doc """
Modifies a column when altering a table.
## Examples
alter table(:posts) do
modify :title, :text
end
## Options
Accepts the same options as `add/3`.
"""
def modify(column, type, opts \\ []) when is_atom(column) do
Runner.subcommand {:modify, column, type, opts}
end
@doc """
Removes a column when altering a table.
## Examples
alter table(:posts) do
remove :title
end
"""
def remove(column) when is_atom(column) do
Runner.subcommand {:remove, column}
end
@doc """
Adds a foreign key.
## Examples
create table(:product) do
add :category_id, references(:category)
end
## Options
* `:column` - The foreign key column, default is `:id`
* `:type` - The foreign key type, default is `:integer`
"""
def references(table, opts \\ []) when is_atom(table) do
struct(%Reference{table: table}, opts)
end
@doc """
Checks if a table or index exists.
## Examples
exists? table(:products)
"""
def exists?(%{} = object) do
Runner.exists?(object)
end
end