Crate barrel

Powerful schema migration builder, that let’s you write your SQL migrations in Rust.

barrel makes writing migrations for different databases as easy as possible. It provides you with a common API over SQL, with certain features only provided for database specific implementations. This way you can focus on your Rust code, and stop worrying about SQL.

barrel has three primary models: the Migration which represents all changes and changes made on a database level, the Table and the Type.

When creating or altering tables a lambda which exposes &mut Table is provided for initialisation. Adding columns is then as easy as calling add_column(...) on the table.

Each column is statically typed and some types require some metadata in order to compile the migration (for example Varchar(255)). You can also provide default types and override encodings, nullability or uniqueness of columns. Some checks are performed at compile-time however most things (including) correct default values) are only checked at runtime.

Note Since version 0.3.0 it is required to provide a database backend in order to compile barrel.

The following code is a simple example of how to get going with barrel

use barrel::{types, Migration};

fn main() {
    let mut m = Migration::new();
    m.create_table("users", |t| {
        t.add_column("name", types::varchar(255));
        t.add_column("age", types::integer());
        t.add_column("owns_plushy_sharks", types::boolean());
    });
}

barrel also supports more advanced types, such as foreign(...) and array(...) however currently doesn’t support nested Array types on foreign keys (such as array(array(foreign(...)))). Each column addition returns a Column object which can then be used to provide further configuration.

To generate SQL strings you have two options. If you just want to run the migration yourself simply run Migration::exec() where you provide a generic SqlGenerator type according to your database backend

// Example for pgsql
m.make::<Pg>();

Alternatively, if you’re a library developer and you want to more easily embed barrel into your library you can simply implement the DatabaseExecutor trait for a type of yours that knows how to execute SQL. Running a migration with barrel is then super easy.

use barrel::connectors::SqlRunner;

struct MyRunner;
impl SqlRunner for MyRunner {
    fn execute<S: Into<String>>(&mut self, sql: S) {
        // ...
    }
}

m.execute::<Pg, _>(&mut executor);

In this case executor is your provided type which implements the required trait. You can read more about this in the connectors module docs.

If you find database-specific features or documentation lacking, don’t hesitate to open an issue/PR about it.

Re-exports

• pub use backend::SqlVariant;
• pub use migration::Migration;
• pub use table::Table;
• pub use table::TableMeta;

Modules

• backend
  A backend module which provides a few generic traits to implement SQL generation for different databases.
• connectors
  A module meant for library developers
• functions
• migration
  Core migration creation handler
• table
  A module that represents tables and columns
• types
  Types constructor module

Enums

• ConstraintChange
  An enum set that represents operations done with and on constraints
• DatabaseChange
  An enum set that represents a single change on a database
• ForeignKeyChange
  An enum set that represents operations done with and on foreign keys
• IndexChange
  An enum set that represents operations done with and on indices
• PrimaryKeyChange
  An enum set that represents operations done to the primary key
• TableChange
  An enum set that represents a single change on a table