Struct PostgresProjectionGenerator 

pub struct PostgresProjectionGenerator { /* private fields */ }

PostgreSQL SQL projection generator using jsonb_build_object.

Generates efficient PostgreSQL SQL that projects only requested JSONB fields, reducing payload size and JSON deserialization time.

Implementations

impl PostgresProjectionGenerator

pub fn new() -> Self

Create new PostgreSQL projection generator with default JSONB column name.

Default JSONB column: “data”

pub fn with_column(jsonb_column: &str) -> Self

Create projection generator with custom JSONB column name.

Arguments

• jsonb_column - Name of the JSONB column in the database table

pub fn generate_projection_sql(&self, fields: &[String]) -> Result<String>

Generate PostgreSQL projection SQL for specified fields.

Generates a jsonb_build_object() call that selects only the requested fields from the JSONB column, drastically reducing payload size.

Arguments

• fields - GraphQL field names to project from JSONB

Returns

SQL fragment that can be used in a SELECT clause, e.g.: jsonb_build_object('id', data->>'id', 'email', data->>'email')

Example

use fraiseql_db::projection_generator::PostgresProjectionGenerator;
let generator = PostgresProjectionGenerator::new();
let fields = vec!["id".to_string(), "email".to_string()];
let sql = generator.generate_projection_sql(&fields)?;
// Returns:
// jsonb_build_object('id', data->>'id', 'email', data->>'email')
assert!(sql.contains("jsonb_build_object"));

Errors

Returns FraiseQLError::Validation if any field name contains characters that cannot be safely included in a SQL projection.

pub fn generate_typed_projection_sql( &self, fields: &[ProjectionField], ) -> Result<String>

Generate type-aware PostgreSQL projection SQL.

Uses -> (JSONB extraction) for composite fields (objects, lists) and ->> (text extraction) for scalar fields. This avoids the unnecessary text→JSON round-trip that occurs when ->> is used for nested objects.

When a composite field carries sub_fields, the generator recurses and emits a nested jsonb_build_object(...) that selects only the requested sub-fields rather than returning the entire blob. Recursion is capped at [MAX_PROJECTION_DEPTH] levels; deeper fields fall back to data->'field'.

Arguments

• fields - Projection fields with type information

Errors

Returns FraiseQLError::Validation if any field name contains characters that cannot be safely included in a SQL projection.

pub fn generate_select_clause( &self, table_alias: &str, fields: &[String], ) -> Result<String>

Generate complete SELECT clause with projection for a table.

Arguments

• table_alias - Table alias or name in the FROM clause
• fields - Fields to project

Returns

Complete SELECT clause, e.g.: SELECT jsonb_build_object(...) as data

Example

use fraiseql_db::projection_generator::PostgresProjectionGenerator;

let generator = PostgresProjectionGenerator::new();
let fields = vec!["id".to_string(), "name".to_string()];
let sql = generator.generate_select_clause("t", &fields).unwrap();
assert!(sql.contains("SELECT"));

Errors

Propagates any error from Self::generate_projection_sql.

Trait Implementations

impl Default for PostgresProjectionGenerator

fn default() -> Self

Returns the “default value” for a type.