diesel/README.md

YAQB (This will not be the real name. Please open PRs with name ideas)

NOTE: You need to be on nightly >= 11/27/2015. Sorry. I hope to work on stable soon

This is an early stage ORM in Rust. It is poorly documented, and rapidly iterating. I would love early feedback on usage. Help in documenting current usage would also be welcomed.

The goal is to take a different approach here. This is not a port of Active Record or Hibernate. This is an attempt to find what a "Rust ORM" is. So far, what that seems to be is something that is statically guaranteed to only allow correct queries, while still feeling high level.

An "incorrect query" includes, but is not limited to:

• Invalid SQL syntax
• Attempting to interpret a column as the wrong type (e.g. reading varchar as i32, treating a nullable column as something other than an option)
• Selecting a column from another table
• Selecting columns that are not used (this doesn't mean that you have to access that field on your struct, but the struct must have that field)

Does it support X?

0.1 progress is tracked on https://github.com/sgrif/yaqb/issues/1

Getting Started

Before you can do anything, you'll first need to set up your table You'll want to specify the columns and tables that exist using the table! macro. Once you've done that, you can already start using the query builder, and pulling out primitives.

Much of the behavior in yaqb comes from traits, and it is recommended that you import yaqb::*. We avoid exporting generic type names, or any bare functions at that level.

#[macro_use]
extern crate yaqb;

use yaqb::*;

table! {
    users {
        id -> Serial,
        name -> VarChar,
        favorite_color -> Nullable<VarChar>,
    }
}

fn users_with_name(connection: &Connection, target_name: &str)
    -> Vec<(i32, String, Option<String>)>
{
    use self::users::dsl::*;
    users.filter(name.eq(target_name))
        .load(connection)
        .unwrap()
        .collect()
}

Note that we're importing users::dsl::* here. This allows us to deal with only the users table, and not have to qualify everything. If we did not have this import, we'd need to put users:: before each column, and reference the table as users::table.

If you want to be able to query for a struct, you'll need to implement the Queriable trait. Luckily, yaqb_codegen can do this for us automatically.

#[derive(Queriable, Debug)]
pub struct User {
    id: i32,
    name: String,
    favorite_color: Option<String>,
}

fn main() {
    let connection = Connection::establish(env!("DATABASE_URL"))
        .unwrap();
    let users: Vec<User> = users::table.load(&connection)
        .unwrap().collect();

    println!("Here are all the users in our database: {:?}", users);
}

Insert

Inserting data requires implementing the Insertable trait. Once again, we can have this be automatically implemented for us by the compiler.

#[insert_into=users]
struct NewUser<'a> {
    name: &'a str,
    favorite_color: Option<&'a str>,
}

fn create_user(connection: &Connection, name: &str, favorite_color: Option<&str>)
  -> DbResult<User>
{
    let new_user = NewUser {
        name: name,
        favorite_color: favorite_color,
    };
    connection.insert(&users::table, &new_user)
        .map(|mut result| result.nth(0).unwrap())
}

insert can return any struct which implements Queriable for the right type. If you don't actually want to use the results, you should call insert_returning_count instead, or the compiler will complain that it can't infer what type you meant to return. You use the same struct for inserting and querying if you'd like, but you'll need to make the id and columns such as timestamps optional when they otherwise wouldn't be. For this reason, you probably want to create a new struct intead.

You might notice that we're having to manually grab the first record that was inserted. That is because insert can also take a slice or Vec of records, and will insert them in a single query. For this reason, insert will always return an Iterator. A helper for this common case will likely be added in the future.

For both #[derive(Queriable)] and #[insertable_into], you can annotate any single field with #[column_name="name"], if the name of your field differs from the name of the column. This annotation is required on all fields of tuple structs. This cannot be used, however, to work around name collisions with keywords that are reserved in Rust, as you cannot have a column with that name. This may change in the future.

#[insert_into=users]
struct NewUser<'a>(
    #[column_name="name"]
    &'a str,
    #[column_name="favorite_color"]
    Option<&'a str>,
)

fn create_user(connection: &Connection, name: &str, favorite_color: Option<&str>)
  -> DbResult<User>
{
    let new_user = NewUser(name, favorite_color);
    connection.insert(&users::table, &new_user)
        .map(|mut result| result.nth(0).unwrap())
}

Update

To update a record, you'll need to call the update function. Unlike insert (which may change to use this pattern in the future), update is a top level function which creates a query that you'll later pass to the Connection. Here's a simple example.

fn change_users_name(connection: &Connection, target: i32, new_name: &str) -> DbResult<User> {
    use yaqb::query_builder::update;
    use users::dsl::*;

    let command = update(users.filter(id.eq(target))).set(name.eq(new_name));
    connection.query_one(&command)
        .map(|r| r.unwrap())
}

Similar to insert, we always return a Result<Option<Model>>, as we can't tell at compile time if this is the kind of query that always returns at least 1 result. This may change in the future.

As with insert, we can return any type which implements Queriable for the right types. If you do not want to use the returned record(s), you should call execute_returning_count instead of query_one or query_all.

You can also use a struct to represent the changes, if it implements AsChangeset. You can generate that from a macro (FIXME: This should be a compiler annotation not long after the time of writing this. If it is later than 12/5/15, please open an issue as I'm being lazy)

changeset! {
    User => users {
        name -> String,
        favorite_color -> Option<String>,
    }
}

fn save_user(connection: &Connection, user: &mut User) -> DbResult<()> {
    let command = update(users::table.filter(users::id.eq(user.id)))
        .set(user);
    let updated_user = try!(connection.query_one(&command)).unwrap();
    *user = updated_user;
    Ok(())
}

Note that even though we've implemented AsChangeset, we still need to specify what records we want to update. There will likely be changes that make it harder to accidentally update the entire table before 1.0.

Delete

Delete works very similarly to update, but does not support returning a record.

fn delete_user(connection: &Connection, user: User) -> DbResult<()> {
    use yaqb::query_builder::delete;
    use users::dsl::*;

    let command = delete(users.filter(id.eq(user.id)));
    let deleted_rows = try!(connection.execute_returning_count(&command));
    debug_assert!(deleted_rows == 1);
    Ok(())
}

FIXME: Replace links to source code with hosted doc pages

How do I do other things?

Take a look at the various files named on what you're trying to do in https://github.com/sgrif/yaqb/tree/master/yaqb_tests/tests. See https://github.com/sgrif/yaqb/blob/master/yaqb_tests/tests/schema.rs for how you can go about getting the data structures set up.