检查空查询集

Question

我想确认这是检查空查询集的正确方法，如果这是我遇到 UNIQUE 约束错误的原因。

syn_check= Synonym.objects.filter(MD.objects.get(**filter_dict), synonym_type=Stype.objects.filter(description=values.capitalize().strip()), synonym_name=key)
if not syn_check:
    print 'unavailable synonym', key, values
    syn = Synonym()
    syn.synonym_type=Stype.objects.filter(description=values.capitalize().strip()
    syn.synonym_name = key.strip()
    syn.save()

我在做什么奇怪的事情吗？我也用过if not syn_check.count()，遇到同样的问题。

这是回溯：

    Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
    utility.execute()
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 377, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/core/management/base.py", line 338, in execute
    output = self.handle(*args, **options)
  File "/home/project/PycharmProjects/project/project/management/commands/back_populate_data.py", line 53, in handle
    loaded_syn = data_loaded_syn4_pubchem(synonym_decoded, filter_dict)
  File "/home/project/PycharmProjects/project/project/lookup_data.py", line 203, in data_loaded_syn4_pubchem
    mol_syn_ob.save()
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/base.py", line 589, in save
    force_update=force_update, update_fields=update_fields)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/base.py", line 617, in save_base
    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/base.py", line 698, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/base.py", line 731, in _do_insert
    using=using, raw=raw)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/manager.py", line 92, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/query.py", line 921, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 921, in execute_sql
    cursor.execute(sql, params)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 81, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/utils.py", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "/home/project/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/backends/sqlite3/base.py", line 485, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.IntegrityError: UNIQUE constraint failed: project_synonym.molecule_id, project_synonym.synonym_name, project_synonym.synonym_type_id

谢谢

Answer 1

在你做的时候检查查询集很好。

if not syn_check:

但是，它并不像它可能的那样有效，您正在从数据库加载所有对象，而您只想知道查询集是否为空。

最好使用count()，

if not syn_check.count():

甚至更好地使用 exists()

if not syn_check.exists():

代码中的问题在于您定义查询集的位置

syn_check = Synonym.objects.filter(MD.objects.get(**filter_dict), synonym_type=Stype.objects.filter(description=values.capitalize().strip()), synonym_name=key)

该filter()方法接受Q 对象作为参数，或关键字参数。将模型实例MD.objects.get(...)作为位置参数传递是没有意义的。