mapper.py 文件源码

def get_by(self, *args, **params):
        """returns a single object instance based on the given key/value criterion. 
        this is either the first value in the result list, or None if the list is 
        empty.

        the keys are mapped to property or column names mapped by this mapper's Table, and the values
        are coerced into a WHERE clause separated by AND operators.  If the local property/column
        names dont contain the key, a search will be performed against this mapper's immediate
        list of relations as well, forming the appropriate join conditions if a matching property
        is located.

        e.g.   u = usermapper.get_by(user_name = 'fred')
        """
        x = self.select_whereclause(self._by_clause(*args, **params), limit=1)
        if len(x):
            return x[0]
        else:
            return None