我有一个可以很好地实例化的模型,但是一旦创建,如果我尝试保存它,我会得到一个 IntegrityError ,说主键必须是唯一的。这是什么原因造成的?
还有其他从 Node 继承的模型,它们给了我同样的问题。
这是我的模型:
class Node(MPTTModel):
title = models.CharField(max_length=255)
parent = models.ForeignKey('self', null=True, blank=True,
related_name='children')
class Book(Node):
isbn13 = models.CharField(max_length=14)
description = models.TextField()
这是它生成的 SQL:
CREATE TABLE "main_node" (
"id" integer NOT NULL PRIMARY KEY,
"title" varchar(255) NOT NULL,
"parent_id" integer,
"type" varchar(1) NOT NULL,
"lft" integer unsigned NOT NULL,
"rght" integer unsigned NOT NULL,
"tree_id" integer unsigned NOT NULL,
"level" integer unsigned NOT NULL
)
;
CREATE TABLE "main_book" (
"node_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "main_node" ("id"),
"isbn13" varchar(14) NOT NULL,
"description" text NOT NULL
)
;
当我尝试保存预先存在的模型实例时会发生什么:
>>> b = Book.objects.create(title='c+ for dummies', isbn13='111-1111111111', description='nt')
>>> b.title='c++ for dummies'
>>> b.save()
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "C:\Users\Jackie\Desktop\Code\ProjectName\main\models.py", line 56, in save
super(Book, self).save(self, *args)
File "C:\Python27\lib\site-packages\django\db\models\base.py", line 460, in save
self.save_base(using=using, force_insert=force_insert, force_update=force_update)
File "C:\Python27\lib\site-packages\django\db\models\base.py", line 553, in save_base
result = manager._insert(values, return_id=update_pk, using=using)
File "C:\Python27\lib\site-packages\django\db\models\manager.py", line 195, in _insert
return insert_query(self.model, values, **kwargs)
File "C:\Python27\lib\site-packages\django\db\models\query.py", line 1436, in insert_query
return query.get_compiler(using=using).execute_sql(return_id)
File "C:\Python27\lib\site-packages\django\db\models\sql\compiler.py", line 791, in execute_sql
cursor = super(SQLInsertCompiler, self).execute_sql(None)
File "C:\Python27\lib\site-packages\django\db\models\sql\compiler.py", line 735, in execute_sql
cursor.execute(sql, params)
File "C:\Python27\lib\site-packages\django\db\backends\util.py", line 34, in execute
return self.cursor.execute(sql, params)
File "C:\Python27\lib\site-packages\django\db\backends\sqlite3\base.py", line 234, in execute
return Database.Cursor.execute(self, query, params)
IntegrityError: PRIMARY KEY must be unique
以下是运行的查询:
>>> for q in connection.queries:
... print q['sql'] + "\n\n"
...
SELECT MAX("main_node"."tree_id") AS "tree_id__max" FROM "main_node"
INSERT INTO "main_node" ("title", "parent_id", "type", "lft", "rght", "tree_id", "level") VALUES (c+
for dummies, None, B, 1, 2, 1, 0)
INSERT INTO "main_book" ("node_ptr_id", "isbn13", "description") VALUES (1, 111-1111111111, nt)
SELECT (1) AS "a" FROM "main_node" WHERE "main_node"."id" = 1 LIMIT 1
UPDATE "main_node" SET "title" = c++ for dummies, "parent_id" = NULL, "type" = B, "lft" = 1, "rght"
= 2, "tree_id" = 1, "level" = 0 WHERE "main_node"."id" = 1
INSERT INTO "main_book" ("node_ptr_id", "isbn13", "description") VALUES (1, 111-1111111111, nt)
为什么在我重新保存已创建的实例时尝试插入 main_book?