Trait Dialect

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pub trait Dialect:
    Send
    + Sync
    + Debug
    + 'static {
Show 24 methods    // Required methods
    fn name(&self) -> &'static str;
    fn quote(&self, identifier: &str) -> String;
    fn placeholder(&self, position: usize) -> String;
    fn column_type(&self, kind: &ColumnType) -> String;
    fn now(&self) -> &'static str;
    fn uuid_default(&self) -> Option<&'static str>;
    fn returning(&self) -> ReturningStyle;
    fn limit_offset(
        &self,
        limit: Option<i64>,
        offset: Option<i64>,
        ordered: bool,
    ) -> String;
    fn current_schema_expression(&self) -> &'static str;
    fn list_tables_sql(&self) -> &'static str;

    // Provided methods
    fn supports_if_not_exists_table(&self) -> bool { ... }
    fn supports_if_not_exists_index(&self) -> bool { ... }
    fn booleans_are_integers(&self) -> bool { ... }
    fn max_identifier_length(&self) -> usize { ... }
    fn migrations_table_sql(&self, table: &str) -> String { ... }
    fn add_column_clause(&self) -> &'static str { ... }
    fn begin_sql(&self) -> &'static str { ... }
    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 disable_foreign_keys_sql(&self) -> Option<&'static str> { ... }
    fn enable_foreign_keys_sql(&self) -> Option<&'static str> { ... }
    fn drop_table_sql(&self, table: &str) -> String { ... }
}

Expand description

The differences between one SQL database and another.

Required Methods§

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

postgres, mysql, sqlserver.

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

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

The identifier has already been validated; this only quotes it.

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

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

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

The type name for a logical column type.

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

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

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

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

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fn returning(&self) -> ReturningStyle

How a generated key comes back from an insert.

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

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

ordered says whether the query already has an order by, because SQL Server’s paging syntax requires one and will not accept paging without.

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

The expression naming the schema this connection is working in.

information_schema is standard; the way you ask “which schema am I in” is not.

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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.

migrate:fresh enumerates and drops rather than running one clever statement, because only PostgreSQL has an anonymous block to put a loop in — and the enumerate-then-drop shape works identically everywhere.

Provided Methods§

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fn supports_if_not_exists_table(&self) -> bool

Whether create table if not exists is understood.

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fn supports_if_not_exists_index(&self) -> bool

Whether create index if not exists is understood.

PostgreSQL has it; MySQL and SQL Server do not, so the schema builder emits a plain create index and a repeated migration would fail — which is correct, since migrations run once.

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fn booleans_are_integers(&self) -> bool

Whether a boolean column really is one.

MySQL stores it as tinyint(1) and SQL Server as bit, so both hand back a number where PostgreSQL hands back a boolean. The row decoder uses this to convert.

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fn max_identifier_length(&self) -> usize

The longest identifier this database accepts.

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

The DDL for the migration tracking table.

The key column has to say primary key: MySQL refuses an auto_increment column that is not one, and a real server is the only thing that will tell you so.

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

How a column is added in an alter table.

PostgreSQL and MySQL say add column; SQL Server rejects the keyword on add while requiring it on drop, which is asymmetric enough that nobody guesses it right.

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

Start a transaction.

T-SQL wants the word transaction; the others are happy with begin alone and reject begin transaction is fine there too, but the bare form is what their documentation uses.

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