Trait BasicAdapter

pub trait BasicAdapter<'vertex> {
    type Vertex: Typename + Clone + Debug + 'vertex;

    // Required methods
    fn resolve_starting_vertices(
        &self,
        edge_name: &str,
        parameters: &EdgeParameters,
    ) -> Box<dyn Iterator<Item = Self::Vertex> + 'vertex>;
    fn resolve_property<V>(
        &self,
        contexts: Box<dyn Iterator<Item = DataContext<V>> + 'vertex>,
        type_name: &str,
        property_name: &str,
    ) -> Box<dyn Iterator<Item = (DataContext<V>, FieldValue)> + 'vertex>
       where V: AsVertex<Self::Vertex> + 'vertex;
    fn resolve_neighbors<V>(
        &self,
        contexts: Box<dyn Iterator<Item = DataContext<V>> + 'vertex>,
        type_name: &str,
        edge_name: &str,
        parameters: &EdgeParameters,
    ) -> Box<dyn Iterator<Item = (DataContext<V>, Box<dyn Iterator<Item = Self::Vertex> + 'vertex>)> + 'vertex>
       where V: AsVertex<Self::Vertex> + 'vertex;
    fn resolve_coercion<V>(
        &self,
        contexts: Box<dyn Iterator<Item = DataContext<V>> + 'vertex>,
        type_name: &str,
        coerce_to_type: &str,
    ) -> Box<dyn Iterator<Item = (DataContext<V>, bool)> + 'vertex>
       where V: AsVertex<Self::Vertex> + 'vertex;

    // Provided method
    fn resolve_typename<V>(
        &self,
        contexts: Box<dyn Iterator<Item = DataContext<V>> + 'vertex>,
        _type_name: &str,
    ) -> Box<dyn Iterator<Item = (DataContext<V>, FieldValue)> + 'vertex>
       where V: AsVertex<Self::Vertex> + 'vertex { ... }
}

A simplified variant of the Adapter trait.

Implementing BasicAdapter provides a “free” Adapter implementation. BasicAdapter gives up a bit of Adapter’s flexibility in exchange for being as simple as possible to implement:

• &str instead of &Arc<str> for all names of types, properties, and edges.
• Simplified function signatures, with only the minimum necessary arguments.
• Automatic handling of the __typename special property.

The easiest way to implement this trait is with the Vertex associated type set to an enum that is #[derive(Debug, Clone, TrustfallEnumVertex)].

Required Associated Types

type Vertex: Typename + Clone + Debug + 'vertex

The type of vertices in the dataset this adapter queries. It’s frequently a good idea to use an Rc<…> type for cheaper cloning here.

Required Methods

fn resolve_starting_vertices( &self, edge_name: &str, parameters: &EdgeParameters, ) -> Box<dyn Iterator<Item = Self::Vertex> + 'vertex>

Produce an iterator of vertices for the specified starting edge.

Starting edges are ones where queries are allowed to begin. They are defined directly on the root query type of the schema. For example, User is the starting edge of the following query:

query {
    User {
        name @output
    }
}

The caller guarantees that:

• The specified edge is a starting edge in the schema being queried.
• Any parameters the edge requires per the schema have values provided.

fn resolve_property<V>( &self, contexts: Box<dyn Iterator<Item = DataContext<V>> + 'vertex>, type_name: &str, property_name: &str, ) -> Box<dyn Iterator<Item = (DataContext<V>, FieldValue)> + 'vertex>

where V: AsVertex<Self::Vertex> + 'vertex,

Resolve the value of a vertex property over an iterator of query contexts.

Each DataContext in the contexts argument has an active vertex, which is either None, or a Some(Self::Vertex) value representing a vertex of type type_name defined in the schema.

This method resolves the property value on that active vertex.

Unlike the Adapter::resolve_property method, this method does not handle the special __typename property. Instead, that property is resolved by the BasicAdapter::resolve_typename method, which has a default implementation using the Typename trait implemented by Self::Vertex.

The caller guarantees that:

• type_name is a type or interface defined in the schema.
• property_name is a property field on type_name defined in the schema.
• When the active vertex is Some(...), it’s a vertex of type type_name: either its type is exactly type_name, or type_name is an interface that the vertex’s type implements.

The returned iterator must satisfy these properties:

• Produce (context, property_value) tuples with the property’s value for that context.
• Produce contexts in the same order as the input contexts iterator produced them.
• Produce property values whose type matches the property’s type defined in the schema.
• When a context’s active vertex is None, its property value is FieldValue::Null.

fn resolve_neighbors<V>( &self, contexts: Box<dyn Iterator<Item = DataContext<V>> + 'vertex>, type_name: &str, edge_name: &str, parameters: &EdgeParameters, ) -> Box<dyn Iterator<Item = (DataContext<V>, Box<dyn Iterator<Item = Self::Vertex> + 'vertex>)> + 'vertex>

where V: AsVertex<Self::Vertex> + 'vertex,

Resolve the neighboring vertices across an edge, for each query context in an iterator.

Each DataContext in the contexts argument has an active vertex, which is either None, or a Some(Self::Vertex) value representing a vertex of type type_name defined in the schema.

This method resolves the neighboring vertices for that active vertex.

If the schema this adapter covers has no edges aside from starting edges, then this method will never be called and may be implemented as unreachable!().

The caller guarantees that:

• type_name is a type or interface defined in the schema.
• edge_name is an edge field on type_name defined in the schema.
• Any parameters the edge requires per the schema have values provided.
• When the active vertex is Some(...), it’s a vertex of type type_name: either its type is exactly type_name, or type_name is an interface that the vertex’s type implements.

The returned iterator must satisfy these properties:

• Produce (context, neighbors) tuples with an iterator of neighbor vertices for that edge.
• Produce contexts in the same order as the input contexts iterator produced them.
• Each neighboring vertex is of the type specified for that edge in the schema.
• When a context’s active vertex is None, it has an empty neighbors iterator.

fn resolve_coercion<V>( &self, contexts: Box<dyn Iterator<Item = DataContext<V>> + 'vertex>, type_name: &str, coerce_to_type: &str, ) -> Box<dyn Iterator<Item = (DataContext<V>, bool)> + 'vertex>

where V: AsVertex<Self::Vertex> + 'vertex,

Attempt to coerce vertices to a subtype, over an iterator of query contexts.

In this example query, the starting vertices of type File are coerced to AudioFile:

query {
    File {
        ... on AudioFile {
            duration @output
        }
    }
}

The ... on AudioFile operator causes only AudioFile vertices to be retained, filtering out all other kinds of File vertices.

Each DataContext in the contexts argument has an active vertex, which is either None, or a Some(Self::Vertex) value representing a vertex of type type_name defined in the schema.

This method checks whether the active vertex is of the specified subtype.

If this adapter’s schema contains no subtyping, then no type coercions are possible: this method will never be called and may be implemented as unreachable!().

The caller guarantees that:

• type_name is an interface defined in the schema.
• coerce_to_type is a type or interface that implements type_name in the schema.
• When the active vertex is Some(...), it’s a vertex of type type_name: either its type is exactly type_name, or type_name is an interface that the vertex’s type implements.

The returned iterator must satisfy these properties:

• Produce (context, can_coerce) tuples showing if the coercion succeded for that context.
• Produce contexts in the same order as the input contexts iterator produced them.
• Each neighboring vertex is of the type specified for that edge in the schema.
• When a context’s active vertex is None, its coercion outcome is false.

Provided Methods

fn resolve_typename<V>( &self, contexts: Box<dyn Iterator<Item = DataContext<V>> + 'vertex>, _type_name: &str, ) -> Box<dyn Iterator<Item = (DataContext<V>, FieldValue)> + 'vertex>

where V: AsVertex<Self::Vertex> + 'vertex,

Resolve the __typename special property over an iterator of query contexts.

Each DataContext in the contexts argument has an active vertex, which is either None, or a Some(Self::Vertex) value representing a vertex of type type_name defined in the schema.

This method resolves the name of the type of that active vertex. That type may not always be the same as the value of the type_name parameter, due to inheritance in the schema. For example, consider a schema with types interface Message and type Email implements Message, and a query like the following:

query {
    Message {
        __typename @output
    }
}

The resulting resolve_typename() call here would have type_name = "Message". However, some of the messages read by this query may be emails! For those messages, outputting __typename would produce the value "Email".

The default implementation uses the Typename trait implemented by Self::Vertex to get each vertex’s type name.

The caller guarantees that:

• type_name is a type or interface defined in the schema.
• When the active vertex is Some(...), it’s a vertex of type type_name: either its type is exactly type_name, or type_name is an interface that the vertex’s type implements.

The returned iterator must satisfy these properties:

• Produce (context, property_value) tuples with the property’s value for that context.
• Produce contexts in the same order as the input contexts iterator produced them.
• Produce property values whose type matches the property’s type defined in the schema.
• When a context’s active vertex is None, its property value is FieldValue::Null.

Overriding the default implementation

Some adapters may be able to implement this method more efficiently than the provided default implementation.

For example: adapters having access to a Schema can use the interpreter::helpers::resolve_typename method, which implements a “fast path” for types that don’t have any subtypes per the schema.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors