Merge pull request #3 from nicheinc/bug/pgx-locking-strategy

Use Postgres.conn rather than Postgres.db to handle table locking

database/pgx/pgx.go

@@ -370,7 +370,7 @@ func (p *Postgres) releaseTableLock() error {
 	}
 
 	query := "DELETE FROM " + pq.QuoteIdentifier(p.config.LockTable) + " WHERE lock_id = $1"
-	if _, err := p.db.Exec(query, aid); err != nil {
+	if _, err := p.conn.ExecContext(context.Background(), query, aid); err != nil {
 		return database.Error{OrigErr: err, Err: "failed to release migration lock", Query: []byte(query)}
 	}
 
@@ -615,15 +615,15 @@ func (p *Postgres) ensureLockTable() error {
 
 	var count int
 	query := `SELECT COUNT(1) FROM information_schema.tables WHERE table_name = $1 AND table_schema = (SELECT current_schema()) LIMIT 1`
-	if err := p.db.QueryRow(query, p.config.LockTable).Scan(&count); err != nil {
+	if err := p.conn.QueryRowContext(context.Background(), query, p.config.LockTable).Scan(&count); err != nil {
 		return &database.Error{OrigErr: err, Query: []byte(query)}
 	}
 	if count == 1 {
 		return nil
 	}
 
 	query = `CREATE TABLE ` + pq.QuoteIdentifier(p.config.LockTable) + ` (lock_id BIGINT NOT NULL PRIMARY KEY)`
-	if _, err := p.db.Exec(query); err != nil {
+	if _, err := p.conn.ExecContext(context.Background(), query); err != nil {
 		return &database.Error{OrigErr: err, Query: []byte(query)}
 	}