Type Alias Migration

pub type Migration = Box<dyn Fn(&Connection) -> CargoResult<()>>;

A function or closure representing a database migration.

Migrations support evolving the schema and contents of the database across new versions of cargo. The migrate function should be called immediately after opening a connection to a database in order to configure the schema. Whether or not a migration has been done is tracked by the pragma_user_version value in the database. Typically you include the initial CREATE TABLE statements in the initial list, but as time goes on you can add new tables or ALTER TABLE statements. The migration code will only execute statements that haven’t previously been run.

Important things to note about how you define migrations:

• Never remove a migration entry from the list. Migrations are tracked by the index number in the list.
• Never perform any schema modifications that would be backwards incompatible. For example, don’t drop tables or columns.

The basic_migration function is a convenience function for specifying migrations that are simple SQL statements. If you need to do something more complex, then you can specify a closure that takes a [Connection] and does whatever is needed.

For example:

migrate(
    &mut conn,
    &[
        basic_migration(
            "CREATE TABLE foo (
                id INTEGER PRIMARY KEY AUTOINCREMENT,
                name STRING NOT NULL
            )",
        ),
        Box::new(|conn| {
            conn.execute("INSERT INTO foo (name) VALUES (?1)", [generate_name()])?;
            Ok(())
        }),
        basic_migration("ALTER TABLE foo ADD COLUMN size INTEGER"),
    ],
)?;

Aliased Type

struct Migration(/* private fields */);

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 16 bytes