defmodule Ecto.Adapters.SQLite3 do
@moduledoc """
Adapter module for SQLite3.
It uses `Exqlite` for communicating to the database.
## Options
The adapter supports a superset of the options provided by the
underlying `Exqlite` driver.
### Provided options
* `:database` - The path to the database. In memory is allowed. You can use
`:memory` or `":memory:"` to designate that.
* `:journal_mode` - Sets the journal mode for the sqlite connection. Can be
one of the following `:delete`, `:truncate`, `:persist`, `:memory`,
`:wal`, or `:off`. Defaults to `:wal`.
* `:temp_store` - Sets the storage used for temporary tables. Default is
`:default`. Allowed values are `:default`, `:file`, `:memory`.
* `:synchronous` - Can be `:extra`, `:full`, `:normal`, or `:off`. Defaults
to `:normal`.
* `:foreign_keys` - Sets if foreign key checks should be enforced or not.
Can be `:on` or `:off`. Default is `:on`.
* `:cache_size` - Sets the cache size to be used for the connection. This is
an odd setting as a positive value is the number of pages in memory to use
and a negative value is the size in kilobytes to use. Default is `-64000`.
* `:cache_spill` - The cache_spill pragma enables or disables the ability of
the pager to spill dirty cache pages to the database file in the middle of
a transaction. By default it is `:on`, and for most applications, it
should remain so.
* `:case_sensitive_like` - whether LIKE is case-sensitive or not. Can be
`:off` or `:on`. Defaults to `:off`.
* `:auto_vacuum` - Defaults to `:none`. Can be `:none`, `:full` or
`:incremental`. Depending on the database size, `:incremental` may be
beneficial.
* `:locking_mode` - Defaults to `:normal`. Allowed values are `:normal` or
`:exclusive`. See [sqlite documentation][1] for more information.
* `:secure_delete` - Defaults to `:off`. Can be `:off` or `:on`. If `:on`, it will cause SQLite3
to overwrite records that were deleted with zeros.
* `:wal_auto_check_point` - Sets the write-ahead log auto-checkpoint
interval. Default is `1000`. Setting the auto-checkpoint size to zero or a
negative value turns auto-checkpointing off.
* `:busy_timeout` - Sets the busy timeout in milliseconds for a connection.
Default is `2000`.
* `:pool_size` - the size of the connection pool. Defaults to `5`.
For more information about the options above, see [sqlite documentation][1]
### Differences between SQLite and Ecto SQLite defaults
For the most part, the defaults we provide above match the defaults that SQLite usually
ships with. However, SQLite has conservative defaults due to its need to be strictly backwards
compatible, so some of them do not necessarily match "best practices". Below are the defaults
we provide above that differ from the normal SQLite defaults, along with rationale.
* `:journal_mode` - we use `:wal`, as it is vastly superior
for concurrent access. SQLite usually defaults to `:delete`.
See [SQLite documentation][2] for more info.
* `:temp_store` - we use `:memory`, which increases performance a bit.
SQLite usually defaults to `:file`.
* `:foreign_keys` - we set it to `:on`, for better relational guarantees.
This is also the default of the underlying `Exqlite` driver.
SQLite usually defaults to `:off` for backwards compat.
* `:busy_timeout` - we set it to `2000`, to better enable concurrent access.
This is also the default of `Exqlite`. SQLite usually defaults to `0`.
* `:cache_size` - we set it to `-64000`, to speed up access of data.
SQLite usually defaults to `-2000`.
These defaults can of course be overridden, as noted above, to suit other needs.
[1]: https://www.sqlite.org/pragma.html
[2]: https://sqlite.org/wal.html
## Limitations and caveats
There are some limitations when using Ecto with SQLite that one needs
to be aware of. The ones listed below are specific to Ecto usage, but it
is encouraged to also view the guidance on [when to use SQLite][4] provided
by the SQLite documentation, as well.
### Async Sandbox testing
The Ecto SQLite3 adapter does not support async tests when used with
`Ecto.Adapters.SQL.Sandbox`. This is due to SQLite only allowing up one
write transaction at a time, which often does not work with the Sandbox approach of
wrapping each test in a transaction.
### LIKE match on BLOB columns
We have the DSQLITE_LIKE_DOESNT_MATCH_BLOBS compile-time option set to true,
as [recommended][3] by SQLite. This means you cannot do LIKE queries on BLOB columns.
### Case sensitivity
Case sensitivty for `LIKE` is off by default, and controlled by the `:case_sensitive_like`
option outlined above.
However, for equality comparison, case sensitivity is always _on_.
If you want to make a column not be case sensitive, for email storage for example, you can
make it case insensitive by using the [`COLLATE NOCASE`][6] option in SQLite. This is configured
via the `:collate` option.
So instead of:
add :email, :string
You would do:
add :email, :string, collate: :nocase
### Check constraints
SQLite3 supports specifying check constraints on the table or on the column definition. We currently only
support adding a check constraint via a column definition, since the table definition approach only
works at table-creation time and cannot be added at table-alter time. You can see more information in
the SQLite3 [CREATE TABLE documentation](https://sqlite.org/lang_createtable.html).
Because of this, you cannot add a constraint via the normal `Ecto.Migration.constraint/3` method, as that
operates via ALTER TABLE ADD CONSTRAINT, and this type of ALTER TABLE operation SQLite3 does not support.
You can however get the full functionality by adding a constraint at the column level, specifying the name
and expression. Per the SQLite3 documentation, there is no _functional_ difference between a column or table constraint.
Thus, adding a check constraint for a new column is as simple as:
add :email, :string, check: %{name: "test_constraint", expr: "email != 'test@example.com')"}
### Handling foreign key constraints in changesets
Unfortunately, unlike other databases, SQLite3 does not provide the precise name of the constraint violated,
but only the columns within that constraint (if it provides any information at all). Because of this, changeset
functions like `Ecto.Changeset.foreign_key_constraint/3` may not work at all.
This is because the above functions depend on the Ecto Adapter returning the name of the violated constraint,
which you annotate in your changeset so that Ecto can convert the constraint violation into the correct
updated changeset when the constraint is hit during a `Ecto.Repo.update/2` or `Ecto.Repo.insert/2` operation.
Since we cannot get the name of the violated constraint back from SQLite3 at `INSERT` or `UPDATE` time,
there is no way to effectively use these changeset functions. This is a SQLite3 limitation.
See [this GitHub issue](https://github.com/elixir-sqlite/ecto_sqlite3/issues/42) for more details.
### Schemaless queries
Using [schemaless Ecto queries][7] will not work well with SQLite. This is because
the Ecto SQLite adapter relies heavily on the schema to support a rich array of Elixir
types, despite the fact SQLite only has [five storage classes][5]. The query will still
work and return data, but you will need to do this mapping on your own.
[3]: https://www.sqlite.org/compile.html
[4]: https://www.sqlite.org/whentouse.html
[5]: https://www.sqlite.org/datatype3.html
[6]: https://www.sqlite.org/datatype3.html#collating_sequences
[7]: https://hexdocs.pm/ecto/schemaless-queries.html
"""
use Ecto.Adapters.SQL,
driver: :exqlite
@behaviour Ecto.Adapter.Storage
@behaviour Ecto.Adapter.Structure
alias Ecto.Adapters.SQLite3.Codec
@impl Ecto.Adapter.Storage
def storage_down(options) do
db_path = Keyword.fetch!(options, :database)
with :ok <- File.rm(db_path) do
File.rm(db_path <> "-shm")
File.rm(db_path <> "-wal")
:ok
else
_ -> {:error, :already_down}
end
end
@impl Ecto.Adapter.Storage
def storage_status(options) do
db_path = Keyword.fetch!(options, :database)
if File.exists?(db_path) do
:up
else
:down
end
end
@impl Ecto.Adapter.Storage
def storage_up(options) do
storage_up_with_path(
Keyword.get(options, :database),
Keyword.get(options, :journal_mode, :wal)
)
end
@impl Ecto.Adapter.Migration
def supports_ddl_transaction?(), do: false
@impl Ecto.Adapter.Migration
def lock_for_migrations(_meta, _options, fun) do
fun.()
end
@impl Ecto.Adapter.Structure
def structure_dump(default, config) do
path = config[:dump_path] || Path.join(default, "structure.sql")
with {:ok, contents} <- dump_schema(config),
{:ok, versions} <- dump_versions(config) do
File.mkdir_p!(Path.dirname(path))
File.write!(path, contents <> versions)
{:ok, path}
else
err -> err
end
end
@impl Ecto.Adapter.Structure
def structure_load(default, config) do
path = config[:dump_path] || Path.join(default, "structure.sql")
case run_with_cmd("sqlite3", [config[:database], ".read #{path}"]) do
{_output, 0} -> {:ok, path}
{output, _} -> {:error, output}
end
end
##
## Loaders
##
@impl Ecto.Adapter
def loaders(:boolean, type) do
[&Codec.bool_decode/1, type]
end
@impl Ecto.Adapter
def loaders(:naive_datetime_usec, type) do
[&Codec.naive_datetime_decode/1, type]
end
@impl Ecto.Adapter
def loaders(:time, type) do
[&Codec.time_decode/1, type]
end
@impl Ecto.Adapter
def loaders(:utc_datetime_usec, type) do
[&Codec.utc_datetime_decode/1, type]
end
@impl Ecto.Adapter
def loaders(:utc_datetime, type) do
[&Codec.utc_datetime_decode/1, type]
end
@impl Ecto.Adapter
def loaders(:naive_datetime, type) do
[&Codec.naive_datetime_decode/1, type]
end
@impl Ecto.Adapter
def loaders(:date, type) do
[&Codec.date_decode/1, type]
end
@impl Ecto.Adapter
def loaders({:map, _}, type) do
[&Codec.json_decode/1, &Ecto.Type.embedded_load(type, &1, :json)]
end
@impl Ecto.Adapter
def loaders({:array, _}, type) do
[&Codec.json_decode/1, type]
end
@impl Ecto.Adapter
def loaders(:map, type) do
[&Codec.json_decode/1, type]
end
@impl Ecto.Adapter
def loaders(:float, type) do
[&Codec.float_decode/1, type]
end
@impl Ecto.Adapter
def loaders(:decimal, type) do
[&Codec.decimal_decode/1, type]
end
@impl Ecto.Adapter
def loaders(:binary_id, type) do
case Application.get_env(:ecto_sqlite3, :binary_id_type, :string) do
:string -> [type]
:binary -> [Ecto.UUID, type]
end
end
@impl Ecto.Adapter
def loaders(:uuid, type) do
case Application.get_env(:ecto_sqlite3, :uuid_type, :string) do
:string -> []
:binary -> [type]
end
end
# when we have an e.g., max(created_date) function
# Ecto does not truly know the return type, hence :maybe
# see Ecto.Query.Planner.collect_fields
@impl Ecto.Adapter
def loaders({:maybe, :naive_datetime}, type) do
[&Codec.naive_datetime_decode/1, type]
end
@impl Ecto.Adapter
def loaders(_, type) do
[type]
end
##
## Dumpers
##
@impl Ecto.Adapter
def dumpers(:binary, type) do
[type, &Codec.blob_encode/1]
end
@impl Ecto.Adapter
def dumpers(:boolean, type) do
[type, &Codec.bool_encode/1]
end
@impl Ecto.Adapter
def dumpers(:decimal, type) do
[type, &Codec.decimal_encode/1]
end
@impl Ecto.Adapter
def dumpers(:binary_id, type) do
case Application.get_env(:ecto_sqlite3, :binary_id_type, :string) do
:string -> [type]
:binary -> [type, Ecto.UUID]
end
end
@impl Ecto.Adapter
def dumpers(:uuid, type) do
case Application.get_env(:ecto_sqlite3, :uuid_type, :string) do
:string -> []
:binary -> [type]
end
end
@impl Ecto.Adapter
def dumpers(:time, type) do
[type, &Codec.time_encode/1]
end
@impl Ecto.Adapter
def dumpers(:utc_datetime, type) do
[type, &Codec.utc_datetime_encode/1]
end
@impl Ecto.Adapter
def dumpers(:utc_datetime_usec, type) do
[type, &Codec.utc_datetime_encode/1]
end
@impl Ecto.Adapter
def dumpers(:naive_datetime, type) do
[type, &Codec.naive_datetime_encode/1]
end
@impl Ecto.Adapter
def dumpers(:naive_datetime_usec, type) do
[type, &Codec.naive_datetime_encode/1]
end
@impl Ecto.Adapter
def dumpers({:array, _}, type) do
[type, &Codec.json_encode/1]
end
@impl Ecto.Adapter
def dumpers({:map, _}, type) do
[&Ecto.Type.embedded_dump(type, &1, :json), &Codec.json_encode/1]
end
@impl Ecto.Adapter
def dumpers(:map, type) do
[type, &Codec.json_encode/1]
end
@impl Ecto.Adapter
def dumpers(_primitive, type) do
[type]
end
##
## HELPERS
##
defp storage_up_with_path(nil, _) do
raise ArgumentError,
"""
No SQLite database path specified. Please check the configuration for your Repo.
Your config/*.exs file should have something like this in it:
config :my_app, MyApp.Repo,
adapter: Ecto.Adapters.SQLite3,
database: "/path/to/sqlite/database"
"""
end
defp storage_up_with_path(db_path, journal_mode) do
if File.exists?(db_path) do
{:error, :already_up}
else
db_path |> Path.dirname() |> File.mkdir_p!()
{:ok, db} = Exqlite.Sqlite3.open(db_path)
:ok = Exqlite.Sqlite3.execute(db, "PRAGMA JOURNAL_MODE = #{journal_mode}")
:ok = Exqlite.Sqlite3.close(db)
end
end
defp dump_versions(config) do
table = config[:migration_source] || "schema_migrations"
# `.dump` command also returns CREATE TABLE which will clash with CREATE we already run in dump_schema
# So we set mode to insert which makes every SELECT statement to issue the result
# as the INSERT statements instead of pure text data.
case run_with_cmd("sqlite3", [
config[:database],
".mode insert #{table}",
"SELECT * FROM #{table}"
]) do
{output, 0} -> {:ok, output}
{output, _} -> {:error, output}
end
end
defp dump_schema(config) do
case run_with_cmd("sqlite3", [config[:database], ".schema"]) do
{output, 0} -> {:ok, output}
{output, _} -> {:error, output}
end
end
defp run_with_cmd(cmd, args) do
unless System.find_executable(cmd) do
raise "could not find executable `#{cmd}` in path, " <>
"please guarantee it is available before running ecto commands"
end
System.cmd(cmd, args, stderr_to_stdout: true)
end
end