Parsing errors returned by *pgxpool.Pool.QueryRow into *pgconn.PgError

[rahulsabbineni]

Firstly - thank you for creating and maintaining this library. For the past month, I've been using pgx v4 (now v5) for a new project and have enjoyed using the library.

I'm looking to catch a Postgres table constraint error in order to return a custom error message to the end user. The recommended approach in the Wiki is to use *pgconn.PgError:

err = conn.QueryRow(context.Background(), "select 1 +").Scan(&greeting)
if err != nil {
    var pgErr *pgconn.PgError
    if errors.As(err, &pgErr) {
        fmt.Println(pgErr.Message) // => syntax error at end of input
        fmt.Println(pgErr.Code) // => 42601
    }
}

I'm using pgxpool and while the error is returned, errors.As returns false, preventing further error handling. I attempted 1) using *pgxpool.Pool.QueryRow and 2) explicitly acquiring a connection via *pgxpool.Pool.Acquire followed by Conn.QueryRow. Both attempts were unsuccessful at parsing the error.

An abbreviated version of my code is:

package main

import (
    "github.com/jackc/pgconn"
    "github.com/jackc/pgx/v5"
    "github.com/jackc/pgx/v5/pgxpool"
)

// Method that is executed
func CreateLog(
    ... // Variable declarations
    env Env,
) (string, error) {
    var logID string
    err := env.Pool.QueryRow(
        context.Background(),
        `
        SELECT app.create_log(
            _user_id     := $1::INT,
            _source_id   := $2::UUID,
            _start_date  := $3::TIMESTAMP WITH TIME ZONE,
            _end_date    := $4::TIMESTAMP WITH TIME ZONE,
            _start_page  := $5::INT,
            _end_page    := $6::INT,
            _title       := $7::VARCHAR,
            _content     := $8::TEXT
        );
        `,
        ...
    ).Scan(&logID)
    fmt.Println(err) // Correctly prints - ERROR: new row for relation "log" violates check constraint "page_constraint" (SQLSTATE 23514)
    var pgErr *pgconn.PgError
    if errors.As(err, &pgErr) {
        fmt.Println(pgErr.Message)
        fmt.Println(pgErr.Code)
    }
    return logID, err
}

I don't know if this is a red herring, but using a type assertion (err.(*pgconn.PgError)) instead of errors.As returns the following error: interface conversion: error is *pgconn.PgError, not *pgconn.PgError (types from different packages). I'm using github.com/jackc/pgx/v5 v5.0.1 and github.com/jackc/pgconn v1.13.0.

As I'm receiving the correct error in err, how do I go about parsing the err into *pgconn.PgError? I'm probably doing something obviously wrong here. Thank you!

[rahulsabbineni]

Ah, after digging into the pgx v5 code more I see that pgconn was made part of pgx now. This is also clearly referenced in the CHANGELOG and the pgconn repository.

If anyone else makes this mistake with v5, you can just import github.com/jackc/pgx/v5/pgconn instead of importing github.com/jackc/pgx/pgconn. The code example in the Wiki works just fine.