src/Soluble/Normalist/Synthetic/Table.php
public function getPrimaryKey()
    {
        if ($this->primary_key === null) {
            $pks = $this->getPrimaryKeys();
            if (count($pks) > 1) {
                throw new Exception\MultiplePrimaryKeysFoundException(__METHOD__ . ": Error getting unique primary key on table, multiple found on table " . $this->prefixed_table);
            }
            $this->primary_key = $pks[0];
        }
        return $this->primary_key;
    }
public function getPrimaryKey()
    {
        if ($this->primary_key === null) {
            $pks = $this->getPrimaryKeys();
            if (count($pks) > 1) {
                throw new Exception\MultiplePrimaryKeysFoundException(__METHOD__ . ": Error getting unique primary key on table, multiple found on table " . $this->prefixed_table);
            }
            $this->primary_key = $pks[0];
        }
        return $this->primary_key;
    }
Return primary key, if multiple primary keys found will
throw an exception

@throws Exception\PrimaryKeyNotFoundException when no pk found
@throws Exception\MultiplePrimaryKeysFoundException when multiple primary keys found
@throws Exception\RuntimeException when it cannot determine primary key on table

@return int|string