Ecto SQL

v3.2.0

Ecto SQL v3.2.0 Ecto.Adapters.SQL View Source

This application provides functionality for working with SQL databases in Ecto.

Built-in adapters

By default, we support the following adapters:

Migrations

Ecto supports database migrations. You can generate a migration with:

$ mix ecto.gen.migration create_posts

This will create a new file inside priv/repo/migrations with the change function. Check Ecto.Migration for more information.

To interface with migrations, developers typically use mix tasks:

If you want to run migrations programatically, see Ecto.Migrator.

SQL sandbox

ecto_sql provides a sandbox for testing. The sandbox wraps each test in a transaction, making sure the tests are isolated and can run concurrently. See Ecto.Adapters.SQL.Sandbox for more information.

Structure load and dumping

If you have an existing database, you may want to dump its existing structure and make it reproducible from within Ecto. This can be achieved with two Mix tasks:

  • mix ecto.load - loads an existing structure into the database
  • mix ecto.dump - dumps the existing database structure to the filesystem

For creating and dropping databases, see mix ecto.create and mix ecto.drop that are included as part of Ecto.

Custom adapters

Developers can implement their own SQL adapters by using Ecto.Adapters.SQL and by implementing the callbacks required by Ecto.Adapters.SQL.Connection for handling connections and performing queries. The connection handling and pooling for SQL adapters should be built using the DBConnection library.

When using Ecto.Adapters.SQL, the following options are required:

  • :driver (required) - the database driver library. For example: :postgrex
  • :migration_lock - the lock to use on migration locks. For example: "FOR UPDATE". It may also be nil (for no lock). The user can still override this by setting :migration_lock in the repository configuration

Link to this section Summary

Functions

query(repo, sql, params \\ [], opts \\ [])

Runs custom SQL query on given repo.

query!(repo, sql, params \\ [], opts \\ [])

Same as query/4 but raises on invalid queries.

stream(repo, sql, params \\ [], opts \\ [])

Returns a stream that runs a custom SQL query on given repo when reduced.

table_exists?(repo, table)

Check if the given table exists.

to_sql(kind, repo, queryable)

Converts the given query to SQL according to its kind and the adapter in the given repository.

Link to this section Functions

Link to this function

query(repo, sql, params \\ [], opts \\ []) View Source 
query(
  Ecto.Repo.t() | Ecto.Adapter.adapter_meta(),
  String.t(),
  [term()],
  Keyword.t()
) ::
  {:ok,
   %{
     :rows => nil | [[term()] | binary()],
     :num_rows => non_neg_integer(),
     optional(atom()) => any()
   }}
  | {:error, Exception.t()}

Runs custom SQL query on given repo.

In case of success, it must return an :ok tuple containing a map with at least two keys:

  • :num_rows - the number of rows affected

  • :rows - the result set as a list. nil may be returned instead of the list if the command does not yield any row as result (but still yields the number of affected rows, like a delete command without returning would)

Options

  • :log - When false, does not log the query

Examples 

iex> Ecto.Adapters.SQL.query(MyRepo, "SELECT $1::integer + $2", [40, 2])
{:ok, %{rows: [[42]], num_rows: 1}}

For convenience, this function is also available under the repository:

iex> MyRepo.query("SELECT $1::integer + $2", [40, 2])
{:ok, %{rows: [[42]], num_rows: 1}}
Link to this function

query!(repo, sql, params \\ [], opts \\ []) View Source 
query!(
  Ecto.Repo.t() | Ecto.Adapter.adapter_meta(),
  String.t(),
  [term()],
  Keyword.t()
) :: %{
  :rows => nil | [[term()] | binary()],
  :num_rows => non_neg_integer(),
  optional(atom()) => any()
}

Same as query/4 but raises on invalid queries.

Link to this function

stream(repo, sql, params \\ [], opts \\ []) View Source 
stream(Ecto.Repo.t(), String.t(), [term()], Keyword.t()) :: Enum.t()

Returns a stream that runs a custom SQL query on given repo when reduced.

In case of success it is a enumerable containing maps with at least two keys:

  • :num_rows - the number of rows affected

  • :rows - the result set as a list. nil may be returned instead of the list if the command does not yield any row as result (but still yields the number of affected rows, like a delete command without returning would)

In case of failure it raises an exception.

If the adapter supports a collectable stream, the stream may also be used as the collectable in Enum.into/3. Behaviour depends on the adapter.

Options

  • :log - When false, does not log the query
  • :max_rows - The number of rows to load from the database as we stream

Examples 

iex> Ecto.Adapters.SQL.stream(MyRepo, "SELECT $1::integer + $2", [40, 2]) |> Enum.to_list()
[%{rows: [[42]], num_rows: 1}]
Link to this function

table_exists?(repo, table) View Source 
table_exists?(Ecto.Repo.t(), table :: String.t()) :: boolean()

Check if the given table exists.

Returns true if the table exists in the repo, otherwise false. The table is checked against the current database/schema in the connection.

Link to this function

to_sql(kind, repo, queryable) View Source 
to_sql(:all | :update_all | :delete_all, Ecto.Repo.t(), Ecto.Queryable.t()) ::
  {String.t(), [term()]}

Converts the given query to SQL according to its kind and the adapter in the given repository.

Examples

The examples below are meant for reference. Each adapter will return a different result:

iex> Ecto.Adapters.SQL.to_sql(:all, repo, Post)
{"SELECT p.id, p.title, p.inserted_at, p.created_at FROM posts as p", []}

iex> Ecto.Adapters.SQL.to_sql(:update_all, repo,
                              from(p in Post, update: [set: [title: ^"hello"]]))
{"UPDATE posts AS p SET title = $1", ["hello"]}

This function is also available under the repository with name to_sql:

iex> Repo.to_sql(:all, Post)
{"SELECT p.id, p.title, p.inserted_at, p.created_at FROM posts as p", []}