Trait diesel::prelude::Connection[][src]

pub trait Connection: SimpleConnection + Sized + Send where
    Self: for<'a> ConnectionGatWorkaround<'a, Self::Backend>, 
{ type Backend: Backend; fn establish(database_url: &str) -> ConnectionResult<Self>; fn transaction<T, E, F>(&mut self, f: F) -> Result<T, E>
    where
        F: FnOnce(&mut Self) -> Result<T, E>,
        E: From<Error>
, { ... }
fn begin_test_transaction(&mut self) -> QueryResult<()> { ... }
fn test_transaction<T, E, F>(&mut self, f: F) -> T
    where
        F: FnOnce(&mut Self) -> Result<T, E>,
        E: Debug
, { ... } }
Expand description

A connection to a database

Associated Types

The backend this type connects to

Required methods

Establishes a new connection to the database

The argument to this method and the method’s behavior varies by backend. See the documentation for that backend’s connection class for details about what it accepts and how it behaves.

Provided methods

Executes the given function inside of a database transaction

If there is already an open transaction, savepoints will be used instead.

If the transaction fails to commit due to a SerializationFailure or a ReadOnlyTransaction a rollback will be attempted. If the rollback succeeds, the original error will be returned, otherwise the error generated by the rollback will be wrapped into an Error::RollbackError and returned. In the second case the connection should be considered broken as it contains a uncommitted unabortable open transaction.

If a nested transaction fails to release the corresponding savepoint a rollback will be attempted. If the rollback succeeds, the original error will be returned, otherwise the error generated by the rollback will be wrapped into an Error::RollbackError and returned.

Example

use diesel::result::Error;

conn.transaction::<_, Error, _>(|conn| {
    diesel::insert_into(users)
        .values(name.eq("Ruby"))
        .execute(conn)?;

    let all_names = users.select(name).load::<String>(conn)?;
    assert_eq!(vec!["Sean", "Tess", "Ruby"], all_names);

    Ok(())
})?;

conn.transaction::<(), _, _>(|conn| {
    diesel::insert_into(users)
        .values(name.eq("Pascal"))
        .execute(conn)?;

    let all_names = users.select(name).load::<String>(conn)?;
    assert_eq!(vec!["Sean", "Tess", "Ruby", "Pascal"], all_names);

    // If we want to roll back the transaction, but don't have an
    // actual error to return, we can return `RollbackTransaction`.
    Err(Error::RollbackTransaction)
});

let all_names = users.select(name).load::<String>(conn)?;
assert_eq!(vec!["Sean", "Tess", "Ruby"], all_names);

Creates a transaction that will never be committed. This is useful for tests. Panics if called while inside of a transaction.

Executes the given function inside a transaction, but does not commit it. Panics if the given function returns an error.

Example

use diesel::result::Error;

conn.test_transaction::<_, Error, _>(|conn| {
    diesel::insert_into(users)
        .values(name.eq("Ruby"))
        .execute(conn)?;

    let all_names = users.select(name).load::<String>(conn)?;
    assert_eq!(vec!["Sean", "Tess", "Ruby"], all_names);

    Ok(())
});

// Even though we returned `Ok`, the transaction wasn't committed.
let all_names = users.select(name).load::<String>(conn)?;
assert_eq!(vec!["Sean", "Tess"], all_names);

Implementors