SQL implementations

sqlimplementation.py

"""
This contains various implementations of SQL functions in python
The two functions are not built for the same context
"""

def hash_join(table1, index1, table2, index2):
    """
    Perform a sql like join operation on two dicts, on the specified indexes
    """
    from collections import defaultdict
    h = defaultdict(list)
    # hash phase
    for s in table1:
        h[s[index1]].append(s)
    # join phase
    return [(s + r) for r in table2 for s in h[r[index2]]]


def select(self, *args, where=lambda e: True):
    """
    Perform an SQL select supporting where clause
    Designed to be used in a class with a json member
    :param args: columns to query
    :param where: a lambda with one argument returning a boolean, functions as where clause
                  each entry in the json will be compared with the where clause
    :return:
    """
    returned_data = []

    if len(args) == 0:
        args = self.json["content"][0].keys()

    # filter out by the where clause
    filtered = filter(where, self.json["content"])

    for entry in filtered:
        filtered_entry = {}
        for arg in args:
            filtered_entry[arg] = entry[arg]

        returned_data.append(filtered_entry)

    return returned_data