Map Types

Protocol Buffers supports map fields (key-value pairs) which are represented as map<key_type, value_type> in .proto files. In this plugin, map types are handled using specialized GraphQL types that preserve the key-value structure while ensuring type safety.

Map Type Representation

When converting Protocol Buffer map types to GraphQL:

1. Each map type is represented as an array of entry objects
2. Each entry object contains a key and a value field
3. Separate types are generated for both input and output contexts

Map Entry Type Naming

The plugin follows specific naming conventions for map entry types based on the field type:

For scalar value types:

• Map entry object types (output types): {ScalarTypeName}MapEntry
• Map entry input types: {ScalarTypeName}MapEntryInput

For message or enum value types:

• Map entry object types (output types): {MapKeyType}_{DescriptorName}MapEntry
• Map entry input types: {MapKeyType}_{DescriptorName}MapEntryInput

Where:

• ScalarTypeName is the Pascal-cased GraphQL scalar type name
• MapKeyType is the scalar type used for the map key (e.g., String, Int)
• DescriptorName is determined by the following rules:
  • If the message/enum has a parent: {PascalCasedParentTypeName}_{PascalCasedMessageOrEnumName}
  • If the message/enum has no parent: {PascalCasedTypeName}

Map Entry Types

Each map entry is represented as an object with:

• key: The key type from the Protocol Buffer map
• value: The value type from the Protocol Buffer map

These types are used when returning map data in queries and mutations.

Example

Given a Protocol Buffer message with a map:

message User {
  string id = 1;
  map<string, string> attributes = 2;
  map<string, Address> addresses = 3;
}

message Address {
  string street = 1;
  string city = 2;
}

The plugin will generate:

1. A StringMapEntry object type for the attributes field (since it uses string values)
2. A StringMapEntryInput input type for the attributes field
3. A String_AddressMapEntry object type for the addresses field (since it uses message values with string keys)
4. A String_AddressMapEntryInput input type for the addresses field
5. The User type will have the fields properly typed as arrays of these entry types

This approach allows for typed key-value operations while maintaining compatibility with GraphQL's type system.