Typed field constants

User::objects(&db)
    .filter(User::name.icontains("john").or(User::email.ends_with("@example.com")))
    .order_by([User::name.asc()])

#[derive(Model)] generates one associated constant per field: pub const name: Field<User, String>. The type parameters encode two things:

• The model, so a Field<Post, _> cannot be used by mistake in a User query.
• The Rust type. Lookups are inherent methods that exist only where they make sense. icontains exists only on Field<M, String>, and comparison operands must implement Operand<M, T>. That means User::age.eq("x") fails to compile.

A filter!(User, name__icontains = "john") macro was considered and rejected. The typed-constant API gives IDE completion, rustdoc, and ordinary compiler errors. A macro would still have to generate these same constants in order to validate field names.

Django __ traversal is Post::author.join(Author::name) (and further hops on the joined handle). There are no keyword arguments in Rust, so name__icontains= is not possible.

Implemented in siderite_orm::expr::{Expr, Field, Operand, Lookup}.

See also

• QuerySets
• Architecture
• QueryPlan IR