Struct ResultProjector 

pub struct ResultProjector { /* private fields */ }

Result projector - high-level result transformation.

Implementations

impl ResultProjector

pub fn new(fields: Vec<String>) -> Self

Create new result projector from field names (no aliases).

pub const fn with_mappings(fields: Vec<FieldMapping>) -> Self

Create new result projector with field mappings (supports aliases).

pub fn with_typename(self, typename: impl Into<String>) -> Self

Set __typename to include in all projected objects.

Per GraphQL spec §2.7, __typename returns the name of the object type. This should be called when the client requests __typename in the selection set.

pub fn project_results( &self, results: &[JsonbValue], is_list: bool, ) -> Result<JsonValue>

Project database results to GraphQL response.

Arguments

• results - Database results as JSONB values
• is_list - Whether the query returns a list

Returns

GraphQL-compatible JSON response

Errors

Returns error if projection fails.

pub fn wrap_in_data_envelope(result: JsonValue, query_name: &str) -> JsonValue

Wrap result in GraphQL data envelope.

Arguments

• result - Projected result
• query_name - Query operation name

Returns

GraphQL response with { "data": { "queryName": result } } structure

pub fn add_typename_only( &self, projected_data: &JsonbValue, typename: &str, ) -> Result<JsonValue>

Add __typename field to SQL-projected data.

For data that has already been projected at the SQL level, we only need to add the __typename field in Rust. This is much faster than projecting all fields since the SQL already filtered to only requested fields.

Arguments

• projected_data - JSONB data already projected by SQL
• typename - GraphQL type name to add

Returns

New JSONB value with __typename field added

Example

let projector = ResultProjector::new(vec!["id".to_string(), "name".to_string()]);
// Database already returned only: { "id": "123", "name": "Alice" }
let result = projector.add_typename_only(
    &JsonbValue::new(json!({ "id": "123", "name": "Alice" })),
    "User"
).unwrap();

// Result: { "id": "123", "name": "Alice", "__typename": "User" }
assert_eq!(result["__typename"], "User");

Errors

Returns FraiseQLError::Validation if the projected data contains a list element that is not a JSON object, making __typename injection impossible.

pub fn wrap_error(error: &FraiseQLError) -> JsonValue

Wrap error in GraphQL error envelope.

Arguments

• error - Error to wrap

Returns

GraphQL error response with { "errors": [...] } structure