Executing SQL query with variable number of named parameters in Golang - sql

Question

So I have this PostgreSQL function, which takes variable number of named arguments and returns list of corresponding items:
CREATE OR REPLACE FUNCTION read_user(
_id BIGINT DEFAULT NULL,
_phone VARCHAR(30) DEFAULT NULL,
_type VARCHAR(15) DEFAULT NULL,
_last VARCHAR(50) DEFAULT NULL,
_first VARCHAR(50) DEFAULT NULL
)
RETURNS setof T_USERS
AS $$
BEGIN
RETURN QUERY
SELECT * FROM T_USERS
WHERE ( id = _id OR _id IS NULL )
AND ( phone = _phone OR _phone IS NULL )
AND ( type = _type OR _type IS NULL )
AND ( last = _last OR _last IS NULL )
AND ( first = _first OR _first IS NULL );
EXCEPTION WHEN others THEN
RAISE WARNING 'Transaction failed and was rolled back';
RAISE NOTICE '% %', SQLERRM, SQLSTATE;
END
$$ LANGUAGE plpgsql;
So I can run polymorphic queries like these:
SELECT read_user(_id := 2);
SELECT read_user(_first := 'John', _last := 'Doe');
In Golang I can make something like:
stmt, err := db.Prepare("SELECT read_user(_id = ?)")
But how can I do the same, but with variable amount of read_user arguments? I'm using pq driver https://github.com/lib/pq.

Answer 1

You can construct your one statement by enumerating all the parameters with their placeholders and then you could pass nil explicitly where you don't have the parameter value.
stmt, err := db.Prepare("SELECT read_user(_id := $1, _phone := $2, _type := $3, _last := $4, _first := $5)")
if err != nil {
// ...
}
stmt.Query(2, nil, nil, nil, nil) // result should be equivalent to `SELECT read_user(_id := 2)`
stmt.Query(nil, nil, nil, "Doe", "John") // result should be equivalent to `SELECT read_user(_first := 'John', _last := 'Doe')`
And if you want to have named parameters in Go as well, you can create a struct type to represent the parameters and a wrapper func that'll map that parameter type's fields into the query:
type readUserParams struct {
Id interface{}
Phone interface{}
Type interface{}
Last interface{}
First interface{}
}
func readUser(p *readUserParams) {
stmt.Query(p.Id, p.Phone, p.Type, p.Last, p.First)
// ...
}
readUser(&readUserParams{Id: 2})
readUser(&readUserParams{First: "John", Last:"Doe"})