Type descriptors​

This section describes how type information for query input and results is encoded. Specifically, this is needed to decode the server response to the DescribeStatement message.

The type descriptor is essentially a list of type information blocks:

• each block encodes one type;

• blocks can reference other blocks.

While parsing the blocks, a database driver can assemble an encoder or a decoder of the EdgeDB binary data.

An encoder is used to encode objects, native to the driver’s runtime, to binary data that EdegDB can decode and work with.

A decoder is used to decode data from EdgeDB native format to data types native to the driver.

There is one special type with type id of zero: 00000000-0000-0000-0000-000000000000. The describe result of this type contains zero blocks. It’s used when a statement returns no meaningful results, e.g. the CREATE DATABASE example statement. It is also used to represent the input descriptor when a query does not receive any arguments.

Set Descriptor​

struct SetDescriptor {
    // Indicates that this is a Set value descriptor.
    uint8   type = 0;
    // Descriptor ID.
    uuid    id;
    // Set element type descriptor index.
    uint16  type_pos;
};

Set values are encoded on the wire as single-dimensional arrays.

Object Shape Descriptor​

struct ObjectShapeDescriptor {
    // Indicates that this is an
    // Object Shape descriptor.
    uint8           type = 1;
    // Descriptor ID.
    uuid            id;
    // Number of elements in shape.
    uint16          element_count;
    ShapeElement    elements[element_count];
};
struct ShapeElement {
    // Field flags:
    //   1 << 0: the field is implicit
    //   1 << 1: the field is a link property
    //   1 << 2: the field is a link
    uint32          flags;
    uint8<Cardinality> cardinality;
    // Field name.
    string          name;
    // Field type descriptor index.
    uint16          type_pos;
};

enum Cardinality {
  NO_RESULT       = 0x6e;
  AT_MOST_ONE     = 0x6f;
  ONE             = 0x41;
  MANY            = 0x6d;
  AT_LEAST_ONE    = 0x4d;
};

Objects are encoded on the wire as tuples.

Base Scalar Type Descriptor​

struct BaseScalarTypeDescriptor {
    // Indicates that this is an
    // Base Scalar Type descriptor.
    uint8           type = 2;
    // Descriptor ID.
    uuid            id;
};

The descriptor IDs for base scalar types are constant. The following table lists all EdgeDB base types descriptor IDs:

Scalar Type Descriptor​

struct ScalarTypeDescriptor {
    // Indicates that this is a
    // Scalar Type descriptor.
    uint8           type = 3;
    // Descriptor ID.
    uuid            id;
    // Parent type descriptor index.
    uint16          base_type_pos;
};

Tuple Type Descriptor​

struct TupleTypeDescriptor {
    // Indicates that this is a
    // Tuple Type descriptor.
    uint8     type = 4;
    // Descriptor ID.
    uuid      id;
    // The number of elements in tuple.
    uint16    element_count;
    // Indexes of element type descriptors.
    uint16    element_types[element_count];
};

An empty tuple type descriptor has an ID of 00000000-0000-0000-0000-0000000000FF.

Named Tuple Type Descriptor​

struct NamedTupleTypeDescriptor {
    // Indicates that this is a
    // Named Tuple Type descriptor.
    uint8        type = 5;
    // Descriptor ID.
    uuid         id;
    // The number of elements in tuple.
    uint16       element_count;
    // Indexes of element type descriptors.
    TupleElement elements[element_count];
};
struct TupleElement {
    // Field name.
    string  name;
    // Field type descriptor index.
    int16   type_pos;
};

Array Type Descriptor​

struct ArrayTypeDescriptor {
    // Indicates that this is an
    // Array Type descriptor.
    uint8        type = 6;
    // Descriptor ID.
    uuid         id;
    // Element type descriptor index.
    uint16       type_pos;
    // The number of array dimensions, at least 1.
    uint16       dimension_count;
    // Sizes of array dimensions, -1 indicates
    // unbound dimension.
    uint32       dimensions[dimension_count];
};

Enumeration Type Descriptor​

struct EnumerationTypeDescriptor {
    // Indicates that this is an
    // Enumeration Type descriptor.
    uint8        type = 7;
    // Descriptor ID.
    uuid         id;
    // The number of enumeration members.
    uint16       member_count;
    // Names of enumeration members.
    string       members[member_count];
};

Scalar Type Name Annotation​

Part of the type descriptor when the Prepare client message has the INLINE_TYPENAMES header set. Every non-builtin base scalar type and all enum types would have their full schema name provided via this annotation.

struct TypeAnnotationDescriptor {
    uint8        type = 0xff;
    // ID of the scalar type.
    uuid         id;
    // Type name.
    string       type_name;
};

Type Annotation Descriptor​

Drivers must ignore unknown type annotations.

struct TypeAnnotationDescriptor {
    // Indicates that this is an
    // Type Annotation descriptor.
    uint8        type = 0x80..0xfe;
    // ID of the descriptor the
    // annotation is for.
    uuid         id;
    // Annotation text.
    string       annotation;
};