防止数据库在 django 和 django-rest-framework 中使用多个 ajax 帖子锁定

Question

我有以下型号

class Peri(models.Model):
    #fields

class Task(models.Model):
    #fields
    peri = models.ForeignKey(Peri)

我正在创建一个 javascript 客户端来创建新的 Peri 和任务。在创建新的 Peri 模型以预先创建必要的任务时，我想对自己轻松一点。每个 Peri 最多有 64 个任务。所以我想预先创建它们，然后让用户从 javascript 客户端/前端编辑它们。创建是使用 ajax 和 django-rest-framework 完成的。我使用 ajax 调用来创建 peri 模型，如果成功，我将创建任务

$.ajax({
    dataType: 'json',
    url: 'api/url',
    data: newPeriInstance,
    success: function (data, textStatus, jqXHR){
        for (var i = 0; i < 64; i++){
            $.ajax({
                dataType:'json',
                data: newTaskInstance,
                url: '/api/url/tasks/',
                success: function (data, textStatus, jqXHR){
                    //code for success
                },
                error: function (jqXHR, textStatus, errorThrown){
                    //code for error
                }
            });
        }
});

问题是我收到锁定数据库的错误。我在开发阶段使用 sqlit，但我不确定这不会在更大的生产规模中发生。我怎样才能通过这个问题？

Internal Server Error: /crm/api/peritasks/
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py", line 114, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/views/decorators/csrf.py", line 57, in wrapped_view
    return view_func(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/rest_framework/viewsets.py", line 79, in view
    return self.dispatch(request, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/rest_framework/views.py", line 403, in dispatch
    response = self.handle_exception(exc)
  File "/usr/local/lib/python2.7/dist-packages/rest_framework/views.py", line 400, in dispatch
    response = handler(request, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/rest_framework/mixins.py", line 54, increate
    self.object = serializer.save(force_insert=True)
  File "/usr/local/lib/python2.7/dist-packages/rest_framework/serializers.py", line 595, in save
    self.save_object(self.object, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/rest_framework/serializers.py", line 1037, in save_object
    obj.save(**kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 545, in save
    force_update=force_update, update_fields=update_fields)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 573, in save_base
    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 654, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 687, in _do_insert
    using=using, raw=raw)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/manager.py", line 232, in _insert
    return insert_query(self.model, objs, fields, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 1511, in insert_query
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py", line 898, in execute_sql
    cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/util.py", line 69, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/util.py", line 53, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/utils.py", line 99, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/util.py", line 53, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/sqlite3/base.py", line 450, in execute
    return Database.Cursor.execute(self, query, params)
OperationalError: database is locked

Answer 1

SQLite does not allow row-level locking 就像许多其他数据库系统一样，这也是它不是最好的开发或生产数据库的众多原因之一。它只支持写操作的数据库级锁，所以当你有多个写入请求时，只允许一个。最终，您肯定会遇到超时或锁定问题，这就是您在此处看到的。

因此，在您的情况下，您有几个选项可以防止锁定。

1. 不要提前创建任务。就初始实现而言，这是最简单的方法，但它需要您的代码库的其余部分能够处理部分或不存在的任务列表。

2. 在创建父对象时创建任务列表。这将需要修改Peri 模型视图的create 方法，但您可以避免客户需要这样做。您可以使用 Django 提供的the bulk_create method 在单个事务中创建所有任务，并且不会遇到很多速度问题。

Answer 2

在 for 循环中发送这么多 Ajax 调用并不是一个好主意。在 Peri 模型中创建任务：

class Peri(models.Model):

    # fields

    def save(self, *args, **kwargs):
        # Create tasks here
        super(Peri, self).save(*args, **kwargs)

Answer 3

虽然存在不预先创建任务的论据，但如果有此要求，您可以扩展当前的 API 视图，使其接受要创建的任务数量（或始终创建 64 个）并构建一个列出并使用 Django 的 bulk_create 方法。

这取决于您从 DRF 使用的 APIView，但作为一个想法：

class MyApiView(baseview):
    def create(*args):
        model = super(MyAPIView, self).create(*args)
        tasks = []
        for i in range(0, 64):
            tasks.append(Task(...))

        Task.objects.bulk_create(tasks)
        return model