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1 from django.contrib.contenttypes.models import ContentType |
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2 |
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3 def fetch_content_objects(tagged_items, select_related_for=None): |
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4 """ |
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5 Retrieves ``ContentType`` and content objects for the given list of |
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6 ``TaggedItems``, grouping the retrieval of content objects by model |
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7 type to reduce the number of queries executed. |
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8 |
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9 This results in ``number_of_content_types + 1`` queries rather than |
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10 the ``number_of_tagged_items * 2`` queries you'd get by iterating |
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11 over the list and accessing each item's ``object`` attribute. |
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12 |
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13 A ``select_related_for`` argument can be used to specify a list of |
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14 of model names (corresponding to the ``model`` field of a |
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15 ``ContentType``) for which ``select_related`` should be used when |
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16 retrieving model instances. |
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17 """ |
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18 if select_related_for is None: select_related_for = [] |
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19 |
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20 # Group content object pks by their content type pks |
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21 objects = {} |
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22 for item in tagged_items: |
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23 objects.setdefault(item.content_type_id, []).append(item.object_id) |
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24 |
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25 # Retrieve content types and content objects in bulk |
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26 content_types = ContentType._default_manager.in_bulk(objects.keys()) |
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27 for content_type_pk, object_pks in objects.iteritems(): |
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28 model = content_types[content_type_pk].model_class() |
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29 if content_types[content_type_pk].model in select_related_for: |
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30 objects[content_type_pk] = model._default_manager.select_related().in_bulk(object_pks) |
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31 else: |
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32 objects[content_type_pk] = model._default_manager.in_bulk(object_pks) |
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33 |
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34 # Set content types and content objects in the appropriate cache |
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35 # attributes, so accessing the 'content_type' and 'object' |
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36 # attributes on each tagged item won't result in further database |
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37 # hits. |
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38 for item in tagged_items: |
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39 item._object_cache = objects[item.content_type_id][item.object_id] |
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40 item._content_type_cache = content_types[item.content_type_id] |