Crates

A crate is a storage backend that implements the Crate!T interface. It defines how data is stored and retrieved — in memory, in MongoDB, from a CSV file, or anywhere else. The framework uses the crate to execute CRUD operations; everything above (routing, middleware, serialization) is handled by the policy and middleware layers.

The Interface

Every crate implements Crate!T, which extends CrateAccess:

interface CrateAccess {
  @safe:
    IQuery get();                      // Query over all items
    IQuery getItem(const string id);   // Query for one item by ID
    Json addItem(const Json item);     // Insert, return with generated ID
    Json updateItem(const Json item);  // Replace by ID, return updated
    void deleteItem(const string id);  // Remove by ID
}

interface Crate(Type) : CrateAccess {
}

Built-In Crates

Crate	Backend	Use Case
MemoryCrate	In-memory array	Testing, prototyping
MongoCrate	MongoDB	Production databases
CrateCache	Decorator	Caching layer over any crate
CsvCrate	CSV file	Flat data import/export

Using a Crate

Create an instance and add it to a router:

auto products = new MemoryCrate!Product;
router.crateSetup!RestApi.add(products);

The framework only cares that your crate implements Crate!T. Routing, middleware, serialization — all handled automatically.

The Query Interface

Crate’s get() and getItem() methods return IQuery, the query builder that operations use for filtering, sorting, and pagination:

interface IQuery {
  @safe:
    IFieldQuery where(string field);
    IQuery sort(string field, int order);  // 1 = ascending, -1 = descending
    IQuery limit(size_t nr);
    IQuery skip(size_t nr);
    InputRange!Json exec();               // Execute and stream results
    size_t size();                         // Count without fetching
}

where() returns IFieldQuery for building conditions:

auto results = crate.get()
  .where("status").equal("active").and()
  .where("score").greaterThan(threshold).and()
  .sort("name", 1)
  .limit(20)
  .exec();

CrateConfig

Every crate accepts a CrateConfig!T that lets you disable specific operations:

auto config = CrateConfig!Product();
config.deleteItem = false;  // No DELETE endpoint generated

auto products = new MongoCrate!Product(collection, config);

Creating Your Own

See Creating a Custom Crate for how to implement a new storage backend.