1 | """ |
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2 | ETLT |
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3 | |||
4 | Copyright 2016 Set Based IT Consultancy |
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5 | |||
6 | Licence MIT |
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7 | """ |
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8 | import abc |
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9 | |||
10 | |||
11 | class RegularDimension(metaclass=abc.ABCMeta): |
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12 | """ |
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13 | Abstract parent class for translating natural key to a technical key of a regular dimension. |
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14 | """ |
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15 | |||
16 | # ------------------------------------------------------------------------------------------------------------------ |
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17 | def __init__(self): |
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18 | """ |
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19 | Object constructor. |
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20 | """ |
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21 | |||
22 | self._map = {} |
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23 | """ |
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24 | The map from natural keys to a technical keys. |
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25 | |||
26 | :type: dict[T, int|None] |
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27 | """ |
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28 | |||
29 | # Pre-load look up data in to the map. |
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30 | self.pre_load_data() |
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31 | |||
32 | # ------------------------------------------------------------------------------------------------------------------ |
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33 | def get_id(self, natural_key, enhancement=None): |
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34 | """ |
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35 | Returns the technical ID for a natural key or None if the given natural key is not valid. |
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36 | |||
37 | :param T natural_key: The natural key. |
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38 | :param T enhancement: Enhancement data of the dimension row. |
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39 | |||
40 | :rtype: int|None |
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41 | """ |
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42 | # If the natural key is known return the technical ID immediately. |
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43 | if natural_key in self._map: |
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44 | return self._map[natural_key] |
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45 | |||
46 | # The natural key is not in the map of this dimension. Call a stored procedure for translating the natural key |
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47 | # to a technical key. |
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48 | self.pre_call_stored_procedure() |
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49 | success = False |
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50 | try: |
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51 | key = self.call_stored_procedure(natural_key, enhancement) |
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52 | success = True |
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53 | finally: |
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54 | self.post_call_stored_procedure(success) |
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55 | |||
56 | # Add the translation for natural key to technical ID to the map. |
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57 | self._map[natural_key] = key |
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58 | |||
59 | return key |
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60 | |||
61 | # ------------------------------------------------------------------------------------------------------------------ |
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62 | @abc.abstractmethod |
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63 | def call_stored_procedure(self, natural_key, enhancement): |
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64 | """ |
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65 | Calls a stored procedure for getting the technical key of a natural key. Returns the technical ID or None if |
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66 | the given natural key is not valid. |
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67 | |||
68 | :param T natural_key: The natural key. |
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69 | :param T enhancement: Enhancement data of the dimension row. |
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70 | |||
71 | :rtype: int|None |
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72 | """ |
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73 | raise NotImplementedError() |
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74 | |||
75 | # ------------------------------------------------------------------------------------------------------------------ |
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76 | def pre_load_data(self): |
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77 | """ |
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78 | Can be overridden to pre-load lookup data from a dimension table. |
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79 | |||
80 | :rtype: None |
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81 | """ |
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82 | pass |
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83 | |||
84 | # ------------------------------------------------------------------------------------------------------------------ |
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85 | def pre_call_stored_procedure(self): |
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86 | """ |
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87 | This method is invoked before call the stored procedure for getting the technical key of a natural key. |
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88 | |||
89 | In a concurrent environment override this method to acquire a lock on the dimension or dimension hierarchy. |
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90 | |||
91 | :rtype: None |
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92 | """ |
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93 | pass |
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94 | |||
95 | # ------------------------------------------------------------------------------------------------------------------ |
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96 | def post_call_stored_procedure(self, success): |
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97 | """ |
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98 | This method is invoked after calling the stored procedure for getting the technical key of a natural key. |
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99 | |||
100 | In a concurrent environment override this method to release a lock on the dimension or dimension hierarchy and |
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101 | to commit or rollback the transaction. |
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102 | |||
103 | :param bool success: If True the stored procedure is executed successfully. If an exception has occurred. |
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104 | |||
105 | :rtype: None |
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106 | """ |
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107 | pass |
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108 | |||
109 | # ---------------------------------------------------------------------------------------------------------------------- |
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110 |