Method executeDatabaseJoinQuery

core/database_join.go:142–242

executeDatabaseJoinQuery executes a query against a target database for a cross-DB join. It builds a GraphQL sub-query for the child table filtered by the parent ID, compiles it using the target database's compilers, and executes it.

(
	ctx context.Context,
	dbCtx *dbContext,
	sel *qcode.Select,
	parentID []byte,
)

// It builds a GraphQL sub-query for the child table filtered by the parent ID,
// compiles it using the target database's compilers, and executes it.
func (s *gstate) executeDatabaseJoinQuery(
	ctx context.Context,
	dbCtx *dbContext,
	sel *qcode.Select,
	parentID []byte,
) ([]byte, error) {
	selects := s.cs.st.qc.Selects

	// Build a GraphQL sub-query for the child table
	fkCol := sel.Rel.Left.Col
	subQuery := buildChildGraphQLQuery(sel, selects, fkCol, parentID)

	// Compile QCode using the target database's compiler
	qc, err := dbCtx.qcodeCompiler.Compile(subQuery, nil, s.role, s.r.namespace)
	if err != nil {
		return nil, fmt.Errorf("qcode compile failed: %w", err)
	}

	if dbCtx.nano != nil {
		raw, err := s.renderNanoDBQuery(dbCtx, qc)
		if err == nil && len(raw) == 0 {
			if sel.Singular {
				raw = []byte(`{"` + sel.Table + `": null}`)
			} else {
				raw = []byte(`{"` + sel.Table + `": []}`)
			}
		}
		return raw, err
	}

	// Compile to SQL using the target database's SQL compiler
	var sqlBuf bytes.Buffer
	md, err := dbCtx.psqlCompiler.Compile(&sqlBuf, qc)
	if err != nil {
		return nil, fmt.Errorf("sql compile failed: %w", err)
	}

	// Get a connection from the target database pool
	conn, err := dbCtx.db.Conn(ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to get connection: %w", err)
	}
	defer conn.Close() //nolint:errcheck

	// Build argument list
	args, err := s.gj.argList(ctx, md, nil, s.r.requestconfig, false, dbCtx.psqlCompiler)
	if err != nil {
		return nil, fmt.Errorf("failed to build args: %w", err)
	}

	// Execute the query
	var data []byte
	querySQL, queryArgs, err := prepareQueryArgsForDB(dbCtx.dbtype, sqlBuf.String(), args.values)
	if err != nil {
		return nil, fmt.Errorf("failed to prepare query args: %w", err)
	}

	cacheKey := s.dbFragmentKey(ctx, fragmentKindDBJoin, dbCtx.name, querySQL, queryArgs, qc)