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1 "Utilities for loading models and the modules that contain them." |
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2 |
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3 from django.conf import settings |
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4 from django.core.exceptions import ImproperlyConfigured |
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5 import sys |
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6 import os |
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7 import threading |
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8 |
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9 __all__ = ('get_apps', 'get_app', 'get_models', 'get_model', 'register_models', |
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10 'load_app', 'app_cache_ready') |
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11 |
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12 class AppCache(object): |
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13 """ |
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14 A cache that stores installed applications and their models. Used to |
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15 provide reverse-relations and for app introspection (e.g. admin). |
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16 """ |
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17 # Use the Borg pattern to share state between all instances. Details at |
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18 # http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/66531. |
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19 __shared_state = dict( |
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20 # Keys of app_store are the model modules for each application. |
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21 app_store = {}, |
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22 |
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23 # Mapping of app_labels to a dictionary of model names to model code. |
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24 app_models = {}, |
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25 |
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26 # Mapping of app_labels to errors raised when trying to import the app. |
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27 app_errors = {}, |
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28 |
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29 # -- Everything below here is only used when populating the cache -- |
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30 loaded = False, |
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31 handled = {}, |
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32 postponed = [], |
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33 nesting_level = 0, |
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34 write_lock = threading.RLock(), |
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35 ) |
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36 |
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37 def __init__(self): |
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38 self.__dict__ = self.__shared_state |
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39 |
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40 def _populate(self): |
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41 """ |
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42 Fill in all the cache information. This method is threadsafe, in the |
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43 sense that every caller will see the same state upon return, and if the |
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44 cache is already initialised, it does no work. |
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45 """ |
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46 if self.loaded: |
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47 return |
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48 self.write_lock.acquire() |
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49 try: |
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50 if self.loaded: |
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51 return |
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52 for app_name in settings.INSTALLED_APPS: |
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53 if app_name in self.handled: |
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54 continue |
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55 self.load_app(app_name, True) |
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56 if not self.nesting_level: |
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57 for app_name in self.postponed: |
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58 self.load_app(app_name) |
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59 self.loaded = True |
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60 finally: |
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61 self.write_lock.release() |
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62 |
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63 def load_app(self, app_name, can_postpone=False): |
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64 """ |
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65 Loads the app with the provided fully qualified name, and returns the |
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66 model module. |
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67 """ |
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68 self.handled[app_name] = None |
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69 self.nesting_level += 1 |
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70 mod = __import__(app_name, {}, {}, ['models']) |
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71 self.nesting_level -= 1 |
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72 if not hasattr(mod, 'models'): |
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73 if can_postpone: |
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74 # Either the app has no models, or the package is still being |
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75 # imported by Python and the model module isn't available yet. |
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76 # We will check again once all the recursion has finished (in |
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77 # populate). |
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78 self.postponed.append(app_name) |
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79 return None |
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80 if mod.models not in self.app_store: |
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81 self.app_store[mod.models] = len(self.app_store) |
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82 return mod.models |
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83 |
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84 def app_cache_ready(self): |
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85 """ |
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86 Returns true if the model cache is fully populated. |
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87 |
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88 Useful for code that wants to cache the results of get_models() for |
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89 themselves once it is safe to do so. |
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90 """ |
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91 return self.loaded |
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92 |
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93 def get_apps(self): |
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94 "Returns a list of all installed modules that contain models." |
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95 self._populate() |
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96 |
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97 # Ensure the returned list is always in the same order (with new apps |
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98 # added at the end). This avoids unstable ordering on the admin app |
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99 # list page, for example. |
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100 apps = [(v, k) for k, v in self.app_store.items()] |
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101 apps.sort() |
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102 return [elt[1] for elt in apps] |
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103 |
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104 def get_app(self, app_label, emptyOK=False): |
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105 """ |
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106 Returns the module containing the models for the given app_label. If |
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107 the app has no models in it and 'emptyOK' is True, returns None. |
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108 """ |
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109 self._populate() |
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110 self.write_lock.acquire() |
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111 try: |
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112 for app_name in settings.INSTALLED_APPS: |
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113 if app_label == app_name.split('.')[-1]: |
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114 mod = self.load_app(app_name, False) |
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115 if mod is None: |
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116 if emptyOK: |
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117 return None |
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118 else: |
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119 return mod |
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120 raise ImproperlyConfigured, "App with label %s could not be found" % app_label |
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121 finally: |
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122 self.write_lock.release() |
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123 |
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124 def get_app_errors(self): |
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125 "Returns the map of known problems with the INSTALLED_APPS." |
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126 self._populate() |
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127 return self.app_errors |
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128 |
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129 def get_models(self, app_mod=None): |
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130 """ |
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131 Given a module containing models, returns a list of the models. |
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132 Otherwise returns a list of all installed models. |
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133 """ |
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134 self._populate() |
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135 if app_mod: |
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136 return self.app_models.get(app_mod.__name__.split('.')[-2], {}).values() |
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137 else: |
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138 model_list = [] |
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139 for app_entry in self.app_models.itervalues(): |
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140 model_list.extend(app_entry.values()) |
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141 return model_list |
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142 |
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143 def get_model(self, app_label, model_name, seed_cache=True): |
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144 """ |
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145 Returns the model matching the given app_label and case-insensitive |
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146 model_name. |
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147 |
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148 Returns None if no model is found. |
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149 """ |
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150 if seed_cache: |
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151 self._populate() |
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152 return self.app_models.get(app_label, {}).get(model_name.lower()) |
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153 |
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154 def register_models(self, app_label, *models): |
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155 """ |
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156 Register a set of models as belonging to an app. |
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157 """ |
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158 for model in models: |
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159 # Store as 'name: model' pair in a dictionary |
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160 # in the _app_models dictionary |
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161 model_name = model._meta.object_name.lower() |
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162 model_dict = self.app_models.setdefault(app_label, {}) |
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163 if model_name in model_dict: |
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164 # The same model may be imported via different paths (e.g. |
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165 # appname.models and project.appname.models). We use the source |
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166 # filename as a means to detect identity. |
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167 fname1 = os.path.abspath(sys.modules[model.__module__].__file__) |
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168 fname2 = os.path.abspath(sys.modules[model_dict[model_name].__module__].__file__) |
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169 # Since the filename extension could be .py the first time and |
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170 # .pyc or .pyo the second time, ignore the extension when |
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171 # comparing. |
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172 if os.path.splitext(fname1)[0] == os.path.splitext(fname2)[0]: |
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173 continue |
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174 model_dict[model_name] = model |
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175 |
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176 cache = AppCache() |
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177 |
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178 # These methods were always module level, so are kept that way for backwards |
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179 # compatibility. |
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180 get_apps = cache.get_apps |
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181 get_app = cache.get_app |
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182 get_app_errors = cache.get_app_errors |
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183 get_models = cache.get_models |
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184 get_model = cache.get_model |
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185 register_models = cache.register_models |
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186 load_app = cache.load_app |
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187 app_cache_ready = cache.app_cache_ready |