Struct Sqlite 

pub struct Sqlite;

SQLite’s SQL.

This dialect compiles unconditionally; the driver beside it does not. A dialect is string formatting with no dependency at all, so the generated SQL can be asserted in a build that cannot open a SQLite file — which is how the other three are tested too.

SQLite is not a server and its SQL reflects that. Three differences are load-bearing:

• Types are advisory. A column has a type affinity, not a type, and a varchar(255) accepts a megabyte. The affinities below are the ones the framework’s ColumnTypes map onto; the lengths are kept in the SQL because they document intent and cost nothing.
• integer primary key is the row id itself, and auto-increments with no keyword. autoincrement exists but only stops row ids being reused after a delete, at the cost of a second table — which is not what the other three do, so it is not asked for here.
• Foreign keys are off unless switched on per connection. That is a SQLite default, not a choice this dialect can make; the driver turns them on for every connection it opens.

Trait Implementations

impl Clone for Sqlite

fn clone(&self) -> Sqlite

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Sqlite

impl Debug for Sqlite

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Sqlite

fn default() -> Sqlite

Returns the “default value” for a type.

impl Dialect for Sqlite

fn skip_locked(&self) -> (&'static str, &'static str)

Nothing, and here that is correct rather than missing. SQLite has no row locks — a write transaction locks the whole database — so two workers cannot both claim one job however the select is written. What makes it safe is begin immediate below, not a clause here.

fn begin_sql(&self) -> &'static str

begin immediate, not the bare begin the other three use.

SQLite’s default transaction is deferred: it takes a read lock on the first select and only tries to upgrade at the first write. Two transactions that both read and then both try to upgrade deadlock, and SQLite breaks the tie by failing one with SQLITE_BUSY immediately — without waiting for busy_timeout, because waiting cannot help. Two queue workers are exactly that shape.

begin immediate takes the write lock up front, so the second worker waits its turn instead of failing.

fn name(&self) -> &'static str

postgres, mysql, sqlserver.

fn quote(&self, identifier: &str) -> String

Wrap one identifier so a keyword or an unusual name is still valid.

fn placeholder(&self, _position: usize) -> String

The placeholder for the position-th bound parameter, counting from 1.

fn column_type(&self, kind: &ColumnType) -> String

The type name for a logical column type.

fn now(&self) -> &'static str

The expression for “now”, used by timestamps().

fn uuid_default(&self) -> Option<&'static str>

The expression that generates a UUID, when the database has one.

fn returning(&self) -> ReturningStyle

How a generated key comes back from an insert.

fn limit_offset( &self, limit: Option<i64>, offset: Option<i64>, _ordered: bool, ) -> String

limit … offset …, in whatever form this database accepts.

fn supports_if_not_exists_index(&self) -> bool

Whether create index if not exists is understood.

fn booleans_are_integers(&self) -> bool

Whether a boolean column really is one.

fn max_identifier_length(&self) -> usize

The longest identifier this database accepts.

fn current_schema_expression(&self) -> &'static str

The expression naming the schema this connection is working in.

fn list_tables_sql(&self) -> &'static str

A query returning one row per table in the current schema, with the name in the first column.

fn disable_foreign_keys_sql(&self) -> Option<&'static str>

Turn off foreign key enforcement while tables are being dropped, so the order they come back in does not matter.

fn enable_foreign_keys_sql(&self) -> Option<&'static str>

fn supports_if_not_exists_table(&self) -> bool

Whether create table if not exists is understood.

fn migrations_table_sql(&self, table: &str) -> String

The DDL for the migration tracking table.

fn add_column_clause(&self) -> &'static str

How a column is added in an alter table.

fn commit_sql(&self) -> &'static str

fn rollback_sql(&self) -> &'static str

fn savepoint_sql(&self, name: &str) -> String

fn rollback_to_savepoint_sql(&self, name: &str) -> String

fn drop_table_sql(&self, table: &str) -> String

Drop one table, including anything depending on it.