{"id":6167,"date":"2022-04-05T18:44:15","date_gmt":"2022-04-05T10:44:15","guid":{"rendered":"https:\/\/egonlin.com\/?p=6167"},"modified":"2022-04-26T13:49:51","modified_gmt":"2022-04-26T05:49:51","slug":"%e7%ac%ac%e5%8d%81%e8%8a%82%ef%bc%9aqueryset%e5%af%b9%e8%b1%a1%e4%b8%8e%e6%9f%a5%e8%af%a2%e4%bc%98%e5%8c%96","status":"publish","type":"post","link":"https:\/\/egonlin.com\/?p=6167","title":{"rendered":"\u7b2c\u5341\u8282\uff1aQuerySet\u5bf9\u8c61\u4e0e\u67e5\u8be2\u4f18\u5316"},"content":{"rendered":"

QuerySet\u5bf9\u8c61\u4e0e\u67e5\u8be2\u4f18\u5316<\/h1>\n

\"\"<\/div><\/p>\n

\u4e00\u3001QuerySet\u5bf9\u8c61<\/h2>\n

Django\u7684ORM\u4e2d\u5b58\u5728\u67e5\u8be2\u96c6\u7684\u6982\u5ff5\u3002<\/p>\n

\u67e5\u8be2\u96c6\uff0c\u4e5f\u79f0\u67e5\u8be2\u7ed3\u679c\u96c6\uff0c\u5373QuerySet\uff0c\u8868\u793a\u4ece\u6570\u636e\u5e93\u4e2d\u83b7\u53d6\u7684\u5bf9\u8c61\u96c6\u5408\u3002<\/p>\n

\u5f53\u8c03\u7528\u5982\u4e0b\u8fc7\u6ee4\u5668\u65b9\u6cd5\u65f6\uff0cDjango\u4f1a\u8fd4\u56de\u67e5\u8be2\u96c6\uff08\u4e0e\u5217\u8868\u7c7b\u4f3c\uff0c\u4f46\u4e0d\u662f\u7b80\u5355\u7684\u5217\u8868\uff09\uff1a<\/p>\n

all()\uff1a\u8fd4\u56de\u6240\u6709\u6570\u636e\u3002\n\nfilter()\uff1a\u8fd4\u56de\u6ee1\u8db3\u6761\u4ef6\u7684\u6570\u636e\u3002\n\nexclude()\uff1a\u8fd4\u56de\u6ee1\u8db3\u6761\u4ef6\u4e4b\u5916\u7684\u6570\u636e\u3002\n\norder_by()\uff1a\u5bf9\u7ed3\u679c\u8fdb\u884c\u6392\u5e8f\u3002<\/code><\/pre>\n
\u67e5\u8be2\u96c6\u6709\u8bf8\u591a\u7279\u6027\uff0c\u6211\u4eec\u6765\u4e00\u4e00\u4e86\u89e3\u5b83\u4eec<\/p>\n
1\u3001\u53ef\u5207\u7247<\/h3>\n
\u53ef\u4ee5\u4f7f\u7528Python \u7684\u5207\u7247\u8bed\u6cd5\u6765\u9650\u5236\u67e5\u8be2\u96c6<\/em>\u8bb0\u5f55\u7684\u6570\u76ee\uff0c\u5b83\u7b49\u540c\u4e8eSQL \u7684LIMIT<\/em> \u548cOFFSET<\/em> \u5b50\u53e5 \u3002<\/p>\n
res = Book.objects.all()[:5]  # limit 5\nprint(res)  # <QuerySet [<Book: book1>, ..., <Book: book5>]>\n\nres = Book.objects.all()[5:7]   # LIMIT 2 OFFSET 5\uff0c\u504f\u79fb5\u6240\u4ee5\u4ece6\u5f00\u59cb\uff0c\u52307\u7ed3\u675f\u5373limit 2\nprint(res)  # <QuerySet [<Book: book6>, <Book: book7>]><\/code><\/pre>\n
\u4e0d\u652f\u6301\u8d1f\u7684\u7d22\u5f15\uff08\u4f8b\u5982Book.objects.all()[-1]<\/em>\uff09\u3002<\/p>\n
*\u5f3a\u8c03\uff1a\u4e0d\u80fd\u628aQuerySet\u5355\u7eaf\u5730\u5f53\u6210python\u4e2d\u7684\u5217\u8868\uff0c\u5b83\u4eec\u8fd8\u662f\u6709\u533a\u522b\u7684\u3002*<\/em><\/strong><\/p>\n
2\u3001\u53ef\u8fed\u4ee3<\/h3>\n
books = Book.objects.all()\nfor book in books:\n    print(book.name)<\/code><\/pre>\n
3\u3001\u60f0\u6027\u67e5\u8be2<\/h3>\n
\u67e5\u8be2\u96c6<\/em> \u662f\u60f0\u6027\u6267\u884c\u7684 \u2014\u2014 \u521b\u5efa\u67e5\u8be2\u96c6<\/em>\u4e0d\u4f1a\u5e26\u6765\u4efb\u4f55\u6570\u636e\u5e93\u7684\u8bbf\u95ee\u3002\u4f60\u53ef\u4ee5\u5c06\u8fc7\u6ee4\u5668\u4fdd\u6301\u4e00\u6574\u5929\uff0c\u76f4\u5230\u67e5\u8be2\u96c6<\/em> \u9700\u8981\u6c42\u503c\u65f6\uff0cDjango \u624d\u4f1a\u771f\u6b63\u8fd0\u884c\u8fd9\u4e2a\u67e5\u8be2\u3002<\/p>\n
query_res = Book.objects.all()  # \u4e0d\u4f1a\u67e5\u8be2\u6570\u636e\u5e93\uff0c\u7ec8\u7aef\u4e5f\u5e76\u65e0sql\u65e5\u5fd7\u6253\u5370\n\nprint(query_res)  # \u6b64\u65f6\u624d\u4f1a\u67e5\u8be2\u6570\u636e\u5e93\uff0c\u5728\u5f00\u542fsql\u65e5\u5fd7\u529f\u80fd\u540e\uff0c\u53ef\u4ee5\u5728\u7ec8\u7aef\u770b\u5230\u6267\u884c\u7684\u539f\u751fsql\n\nfor book in query_res:\n    print(book.name)  # \u6b64\u65f6\u4f1a\u518d\u6b21\u67e5\u8be2\u6570\u636e\u5e93<\/code><\/pre>\n
\u4e00\u822c\u6765\u8bf4\uff0c\u53ea\u6709\u5728\u201c\u8bf7\u6c42\u201d\u67e5\u8be2\u96c6<\/em> \u7684\u7ed3\u679c\u65f6\u624d\u4f1a\u5230\u6570\u636e\u5e93\u4e2d\u53bb\u83b7\u53d6\u5b83\u4eec\u3002\u5f53\u4f60\u786e\u5b9e\u9700\u8981\u7ed3\u679c\u65f6\uff0c\u67e5\u8be2\u96c6<\/em> \u901a\u8fc7\u8bbf\u95ee\u6570\u636e\u5e93\u6765\u6c42\u503c<\/strong><\/p>\n
4\u3001\u7f13\u5b58\u673a\u5236<\/h3>\n
\u6bcf\u4e2a\u67e5\u8be2\u96c6<\/em>\u90fd\u5305\u542b\u4e00\u4e2a\u7f13\u5b58\u6765\u6700\u5c0f\u5316\u5bf9\u6570\u636e\u5e93\u7684\u8bbf\u95ee\u3002\u7406\u89e3\u5b83\u662f\u5982\u4f55\u5de5\u4f5c\u7684\u5c06\u8ba9\u4f60\u7f16\u5199\u6700\u9ad8\u6548\u7684\u4ee3\u7801\u3002<\/p>\n
\u5728\u4e00\u4e2a\u65b0\u521b\u5efa\u7684\u67e5\u8be2\u96c6<\/em>\u4e2d\uff0c\u7f13\u5b58\u4e3a\u7a7a\u3002<\/p>\n
\u5f53\u6211\u4eec\u9996\u6b21\u5bf9\u67e5\u8be2\u96c6<\/em>\u8fdb\u884c\u6c42\u503c\u65f6–\u540c\u65f6\u53d1\u751f\u6570\u636e\u5e93\u67e5\u8be2 \uff0cDjango \u5c06\u67e5\u8be2\u7684\u7ed3\u679c\u4fdd\u5b58\u5230\u67e5\u8be2\u96c6<\/em>\u7684\u7f13\u5b58\u4e2d\u5e76\u8fd4\u56de\u660e\u786e\u8bf7\u6c42\u7684\u7ed3\u679c\u3002\u63a5\u4e0b\u6765\u5bf9\u8be5\u67e5\u8be2\u96c6<\/em> \u7684\u6c42\u503c\u5c06\u91cd\u7528\u7f13\u5b58\u7684\u7ed3\u679c\u3002<\/p>\n
\u8bf7\u7262\u8bb0\u8fd9\u4e2a\u7f13\u5b58\u884c\u4e3a\uff0c\u56e0\u4e3a\u5bf9\u67e5\u8be2\u96c6<\/em>\u4f7f\u7528\u4e0d\u5f53\u7684\u8bdd\uff0c\u5b83\u4f1a\u5751\u4f60\u7684\u3002<\/p>\n
\u4f8b\u5982\uff0c\u4e0b\u9762\u7684\u4e24\u6761\u8bed\u53e5\u67e5\u51fa\u7684\u90fd\u662f\u6240\u6709\u7684\u4e66\u7c4d\uff0c\u4f46\u662f\u6bcf\u6761\u90fd\u521b\u5efa\u4e86\u65b0\u7684\u67e5\u8be2\u96c6<\/em>\uff0c\u7136\u540e\u5404\u81ea\u5bf9\u5404\u81ea\u7684\u67e5\u8be2\u96c6\u6c42\u503c\uff0c\u8fd9\u5b58\u5728\u4e24\u5927\u95ee\u9898<\/p>\n
\u2022 1\u3001\u76f8\u540c\u7684\u6570\u636e\u5e93\u67e5\u8be2\u5c06\u6267\u884c\u4e24\u6b21\uff0c\u663e\u7136\u500d\u589e\u4e86\u4f60\u7684\u6570\u636e\u5e93\u8d1f\u8f7d\u3002<\/p>\n
\u2022 2\u3001\u8fd8\u6709\u53ef\u80fd\u4e24\u4e2a\u7ed3\u679c\u5217\u8868\u5e76\u4e0d\u5305\u542b\u76f8\u540c\u7684\u6570\u636e\u5e93\u8bb0\u5f55\uff0c\u56e0\u4e3a\u5728\u4e24\u6b21\u8bf7\u6c42\u671f\u95f4\u6709\u53ef\u80fd\u6709Article\u88ab\u6dfb\u52a0\u8fdb\u6765\u6216\u5220\u9664\u6389\u3002<\/p>\n
print([book.name for book in Book.objects.all()])\nprint([book.price for book in Book.objects.all()])<\/code><\/pre>\n
\u4e3a\u4e86\u907f\u514d\u4e0a\u8ff0\u95ee\u9898\uff0c\u53ea\u9700\u4fdd\u5b58\u67e5\u8be2\u96c6<\/em>\u5e76\u91cd\u65b0\u4f7f\u7528\u5b83\uff0c\u5982\u4e0b<\/p>\n
# 1\u3001\u5148\u4fdd\u5b58\u7ed3\u679c\u96c6\nquery_res = Book.objects.all()  \n\n# 2\u3001\u7136\u540e\u518d\u5bf9\u7ed3\u679c\u96c6\u8fdb\u884c\u6c42\u503c\nprint([book.name for book in query_res])  # \u9996\u6b21\u5bf9\u67e5\u8be2\u96c6\u6c42\u503c\uff0c\u4f1a\u67e5\u8be2\u6570\u636e\u5e93\u5e76\u7f13\u5b58\nprint([book.price for book in query_res]) # \u547d\u4e2d\u7f13\u5b58\uff0c\u65e0\u9700\u67e5\u8be2\u6570\u636e\u5e93<\/code><\/pre>\n
5\u3001\u4f55\u65f6\u67e5\u8be2\u96c6\u4e0d\u4f1a\u88ab\u7f13\u5b58?<\/h3>\n
1\u3001\u53ea\u6709\u5728\u5bf9\u67e5\u8be2\u96c6\u6c42\u503c\u540e\u624d\u4f1a\u7f13\u5b58<\/p>\n
\u5982\u4e0b\u64cd\u4f5c\u90fd\u7b97\u662f\u5728\u5bf9\u67e5\u8be2\u96c6\u6c42\u503c\uff0c\u5b83\u4eec\u4f1a\u4f7f\u5f97\u5168\u90e8\u7684\u67e5\u8be2\u96c6\u88ab\u6c42\u503c\u5e76\u586b\u5145\u5230\u7f13\u5b58\u4e2d\uff1a<\/p>\n
[book for book in query_res]\nbool(query_res)\nany_obj in query_res\nlist(query_res)\n\nfor obj in query_res:\n    print('\u54ea\u6015\u53ea\u904d\u5386\u4e00\u6b21\uff0c\u4e5f\u7b97\u662f\u5bf9\u67e5\u8be2\u96c6\u6c42\u503c\u4e86\uff0c\u4f1a\u7f13\u5b58Book.objects.all()\u7684\u6240\u6709\u7ed3\u679c')\n    break<\/code><\/pre>\n
2\u3001\u5355\u7eaf\u7684\u6253\u5370\u7ed3\u679c\u96c6\u4e0d\u7b97\u662f\u5bf9\u67e5\u8be2\u96c6\u6c42\u503c\uff0c\u6240\u4ee5\u4e0d\u4f1a\u88ab\u7f13\u5b58\uff0c\u6bcf\u6b21\u6253\u5370\u90fd\u4f1a\u5f15\u53d1\u65b0\u7684\u6570\u636e\u5e93\u67e5\u8be2<\/p>\n
query_res = Book.objects.all()\nprint(query_res)  # \u67e5\u8be2\u6570\u636e\u5e93\nprint(query_res)  # \u67e5\u8be2\u6570\u636e\u5e93<\/code><\/pre>\n
3\u3001\u4f7f\u7528\u5207\u7247\u6216\u7d22\u5f15\u6765\u9650\u5236\u67e5\u8be2\u96c6\u4e5f\u4e0d\u7b97\u662f\u5bf9\u67e5\u8be2\u96c6\u6c42\u503c\uff0c\u6240\u4ee5\u4e5f\u4e0d\u4f1a\u88ab\u7f13\u5b58<\/p>\n
query_res = Book.objects.all()\nprint(query_res[5])  # \u67e5\u8be2\u6570\u636e\u5e93\nprint(query_res[3:5])  # \u67e5\u8be2\u6570\u636e\u5e93<\/code><\/pre>\n
\u6240\u4ee5\uff0c\u6211\u4eec\u53ef\u4ee5\u5148\u5bf9\u67e5\u8be2\u96c6\u6c42\u503c\uff0c\u7f13\u5b58\u597d\u6570\u636e\u4e4b\u540e\u518d\u8fdb\u884c\u4e0a\u8ff02\u548c3\u7684\u64cd\u4f5c<\/p>\n
query_res = Book.objects.all()\n\n123 in query_res  # \u5bf9\u67e5\u8be2\u96c6\u6c42\u503c\uff0c\u4f1a\u67e5\u8be2\u6570\u636e\u5e93\u5e76\u7f13\u5b58\n\nprint(query_res)  # \u547d\u4e2d\u7f13\u5b58\nprint(query_res[5])  # \u547d\u4e2d\u7f13\u5b58\nprint(query_res[3:5])  # \u547d\u4e2d\u7f13\u5b58<\/code><\/pre>\n
6\u3001exists()\u4e0eiterator()\u65b9\u6cd5<\/h3>\n
\u7b80\u5355\u7684\u4f7f\u7528if\u8bed\u53e5\u8fdb\u884c\u5224\u65ad\u4e5f\u4f1a\u5b8c\u5168\u6267\u884c\u6574\u4e2aqueryset\u5e76\u4e14\u628a\u6570\u636e\u653e\u5165cache\uff0c\u5982\u4e0b<\/p>\n
query_res = Book.objects.all()\nif query_res:  # \u67e5\u8be2\u6570\u636e\u5e93\u5e76\u7f13\u5b58\n    print('ok')\n\nprint(query_res)  # \u547d\u4e2d\u7f13\u5b58<\/code><\/pre>\n
\u82e5\u4ec5\u4ec5\u53ea\u9700\u8981\u5224\u65ad\u662f\u5426\u5b58\u5728\u6570\u636e\uff0c\u90a3\u4e48\u518d\u628a\u6240\u6709\u6570\u636e\u96c6\u5408\u90fd\u67e5\u8be2\u56de\u6765\u7f13\u5b58\u5c06\u4f1a\u6781\u5927\u5730\u964d\u4f4e\u6548\u7387\uff0c\u6b64\u65f6\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528exists()\uff0c\u53ea\u62ff\u56de\u6765\u4e00\u6761\u6765\u5224\u65ad\u662f\u5426\u5b58\u5728\u5373\u53ef\uff0c\u9700\u8981\u62ff\u6240\u6709\uff0c\u5f53\u7136\u4e5f\u4e0d\u4f1a\u7f13\u5b58<\/p>\n
query_res = Book.objects.all()\nif query_res.exists():  # \u67e5\u8be2\u6570\u636e\u5e93\uff0c\u4f46\u4e0d\u7f13\u5b58\n    # SELECT (1) AS `a` FROM `app01_book`  LIMIT 1\n    print('ok')\n\nprint(query_res)  # \u65e0\u6cd5\u547d\u4e2d\u4efb\u4f55\u7f13\u5b58\uff0c\u9700\u8981\u518d\u6b21\u67e5\u8be2\u6570\u636e\u5e93<\/code><\/pre>\n
\u5f53queryset\u975e\u5e38\u5de8\u5927\u65f6\uff0ccache\u4f1a\u6210\u4e3a\u95ee\u9898\u3002<\/p>\n
\u5904\u7406\u6210\u5343\u4e0a\u4e07\u7684\u8bb0\u5f55\u65f6\uff0c\u5c06\u5b83\u4eec\u4e00\u6b21\u88c5\u5165\u5185\u5b58\u662f\u5f88\u6d6a\u8d39\u7684\u3002\u66f4\u7cdf\u7cd5\u7684\u662f\uff0c\u5de8\u5927\u7684queryset\u53ef\u80fd\u4f1a\u9501\u4f4f\u7cfb\u7edf \u8fdb\u7a0b\uff0c\u8ba9\u4f60\u7684\u7a0b\u5e8f\u6fd2\u4e34\u5d29\u6e83\u3002\u8981\u907f\u514d\u5728\u904d\u5386\u6570\u636e\u7684\u540c\u65f6\u4ea7\u751fqueryset cache\uff0c\u53ef\u4ee5\u4f7f\u7528iterator()\u65b9\u6cd5 \u6765\u83b7\u53d6\u6570\u636e\uff0citerator\u5e76\u4e0d\u4f1a\u4ea7\u751f\u7f13\u5b58\uff0c\u5904\u7406\u5b8c\u6570\u636e\u540e\u5c31\u4e22\u5f03\u4e86\uff0c\u8981\u60f3\u91cd\u65b0\u83b7\u53d6\u6570\u636e\u5f97\u91cd\u65b0\u62ff\u5230iterator()\uff0c\u5982\u4e0b\u6240\u793a\u3002<\/p>\n
books = Book.objects.all().iterator()\n# iterator()\u53ef\u4ee5\u4e00\u6b21\u53ea\u4ece\u6570\u636e\u5e93\u83b7\u53d6\u5c11\u91cf\u6570\u636e\uff0c\u8fd9\u6837\u53ef\u4ee5\u8282\u7701\u5185\u5b58\n\nfor obj in books:\n    print(obj.name)\n\n#\u5f3a\u8c03:\u518d\u6b21\u904d\u5386\u6ca1\u6709\u6253\u5370,\u56e0\u4e3a\u8fed\u4ee3\u5668\u5df2\u7ecf\u5728\u4e0a\u4e00\u6b21\u904d\u5386(next)\u5230\u6700\u540e\u4e00\u6b21\u4e86,\u6ca1\u5f97\u904d\u5386\u4e86\nfor obj in books:\n    print(obj.name)<\/code><\/pre>\n
\u6ce8\u610f\uff1a\u4f7f\u7528iterator()\u65b9\u6cd5\u6765\u9632\u6b62\u751f\u6210cache\uff0c\u610f\u5473\u7740\u904d\u5386\u540c\u4e00\u4e2aqueryset\u65f6\u4f1a\u91cd\u590d\u6267\u884c\u67e5\u8be2\u3002\u6240\u4ee5\u4f7f\u7528iterator()\u7684\u65f6\u5019\u8981\u5f53\u5fc3\uff0c\u786e\u4fdd\u4f60\u7684\u4ee3\u7801\u5728\u64cd\u4f5c\u4e00\u4e2a\u5927\u7684queryset\u65f6\u6ca1\u6709\u91cd\u590d\u6267\u884c\u67e5\u8be2\u3002<\/p>\n
*\u603b\u7ed3:*<\/em><\/strong><\/p>\n
queryset\u7684cache\u662f\u7528\u4e8e\u51cf\u5c11\u7a0b\u5e8f\u5bf9\u6570\u636e\u5e93\u7684\u67e5\u8be2\uff0c\u5728\u901a\u5e38\u7684\u4f7f\u7528\u4e0b\u4f1a\u4fdd\u8bc1\u53ea\u6709\u5728\u9700\u8981\u7684\u65f6\u5019\u624d\u4f1a\u67e5\u8be2\u6570\u636e\u5e93\u3002 \u4f7f\u7528exists()\u548citerator()\u65b9\u6cd5\u53ef\u4ee5\u4f18\u5316\u7a0b\u5e8f\u5bf9\u5185\u5b58\u7684\u4f7f\u7528\u3002\u4e0d\u8fc7\uff0c\u7531\u4e8e\u5b83\u4eec\u5e76\u4e0d\u4f1a\u751f\u6210queryset cache\uff0c\u53ef\u80fd \u4f1a\u9020\u6210\u989d\u5916\u7684\u6570\u636e\u5e93\u67e5\u8be2\u3002<\/p>\n
\u4e8c\u3001\u8de8\u8868\u67e5\u8be2\u4f18\u5316<\/h2>\n
select_related()<\/h4>\n
\uff081\uff09\u7b80\u5355\u4f7f\u7528<\/h4>\n
\u5bf9\u4e8e\u4e00\u5bf9\u4e00\u5b57\u6bb5\uff08OneToOneField\uff09\u548c\u5916\u952e\u5b57\u6bb5\uff08ForeignKey\uff09\uff0c\u53ef\u4ee5\u4f7f\u7528select_related \u6765\u5bf9QuerySet\u8fdb\u884c\u4f18\u5316\uff0cselect_related\u5e95\u5c42\u5c31\u662f\u94fe\u8868\u64cd\u4f5c<\/p>\n
\u7b80\u5355\u8bf4\uff0c\u5728\u5bf9QuerySet\u4f7f\u7528select_related()\u51fd\u6570\u540e\uff0cDjango\u4f1a\u83b7\u53d6\u76f8\u5e94\u5916\u952e\u5bf9\u5e94\u7684\u5bf9\u8c61\uff0c\u4ece\u800c\u5728\u4e4b\u540e\u9700\u8981\u7684\u65f6\u5019\u4e0d\u5fc5\u518d\u67e5\u8be2\u6570\u636e\u5e93\u4e86\uff0c\u4f8b\u5982<\/p>\n
res = Book.objects.all()\nfor obj in res:\n    print(obj.publish.name)  # \u6bcf\u6b21\u6267\u884c\u8be5\u884c\u4ee3\u7801\u90fd\u4f1a\u89e6\u53d1\u65b0\u7684sql\u6267\u884c\uff0c\u6548\u7387\u6781\u4f4e\n"""\n\u5e95\u5c42\u4f1a\u5148\u53bbbook\u8868\u91cc\u67e5\u51fa\u6240\u6709\u7684\u4e66\u7c4did\n\u7136\u540e\u6bcf\u6b21for\u5faa\u73af\u90fd\u4f1a\u62ff\u7740\u4e00\u4e2a\u4e66\u7c4d\u7684id\u53bbpublish\u8868\u91cc\u67e5\u5230\u5bf9\u5e94\u51fa\u7248\u793e\u7684\u540d\u5b57\n"""    \n\n# \u4f18\u5316\nres = Book.objects.select_related('publish')  \n\nfor obj in res:\n    print(obj.publish.name)\n"""\n\u5e95\u5c42\u4f1a\u5148\u5c06Book\u4e0ePublish\u5bf9\u5e94\u7684\u4e24\u5f20\u8868\u8fde\u63a5\u6210\u4e00\u5f20\u5927\u8868\uff0c\u7136\u540e\u4e00\u6b21\u6027\u5c06\u5927\u8868\u7684\u6240\u6709\u6570\u636e\u4e00\u6b21\u6027\u5c01\u88c5\u7ed9\u67e5\u8be2\u51fa\u6765\u7684\u5bf9\u8c61\n    \u6b64\u65f6\u5bf9\u8c61\u65e0\u8bba\u662f\u70b9\u51fbbook\u8868\u7684\u6570\u636e\u8fd8\u662fpublish\u8868\u7684\u6570\u636e\u90fd\u65e0\u9700\u518d\u8d70\u989d\u5916\u7684\u6570\u636e\u5e93\u67e5\u8be2\u4e86\n"""\n\nfor obj in res:\n    print(obj.publish.city)\n"""\n\u7b2c\u4e8c\u6b21for\u5faa\u73af\u76f4\u63a5\u4f7f\u7528\u4e0a\u8ff0\u7f13\u5b58\u5373\u53ef\n"""<\/code><\/pre>\n
\u4f46\u9700\u8981\u6ce8\u610f\u7684\u662f\uff1aselect_related()\u62ec\u53f7\u5185\u53ea\u80fd\u653e\u5916\u952eForeignkey\u5b57\u6bb5<\/p>\n
\u56e0\u4e3a\u4e00\u5bf9\u591a\u3001\u4e00\u5bf9\u4e00\u5173\u7cfb\u5747\u4f7f\u7528ForeignKey\uff0c\u800c\u591a\u5bf9\u591a\u5219\u4e0d\u662f\uff0c\u6240\u4ee5select_related\u4e0d\u652f\u6301\u591a\u5bf9\u591a\u5173\u7cfb\uff0c\u82e5\u60f3\u4f18\u5316\u591a\u5bf9\u591a\u7684\u67e5\u8be2\u8bf7\u770b\u4e0b\u4e00\u5c0f\u8282 \uff082\uff09\u591a\u5916\u952e\u67e5\u8be2<\/p>\n
\u5982\u679c\u4e00\u4e2a\u6a21\u578b\u4e2d\u5b58\u5728\u591a\u4e2aForeignKey\u5b57\u6bb5<\/p>\n
res = Book.objects.select_related("publish")\n\n\u6b64\u65f6\u6211\u4eec\u67e5\u8be2publish\u76f8\u5173\u7684\u65f6\u5019\uff0c\u4e0d\u4f1a\u91cd\u590d\u67e5\u8be2\uff0c\u5982\u4e0b\nfor obj in res:\n    print(obj.publish.name)\n\nfor obj in res:\n    print(obj.publish.city)\n\n\u4f46\u5982\u679c\u6211\u4eec\u67e5\u8be2\u7684\u662fBook\u5185\u7684\u5176\u4ed6ForeignKey\u5b57\u6bb5\uff0c\u8fd8\u662f\u4f1a\u91cd\u65b0\u67e5\u8be2\nfor obj in res:\n    print(obj.other_fk.attr)\n\n# \u89e3\u51b3\u65b9\u6848\u5c31\u662f\nres = Book.objects.select_related("publish","other_fk")\n\n\u6216\u8005\u4f7f\u7528django1.7\u4e4b\u540e\u652f\u6301\u7684\u94fe\u5f0f\u64cd\u4f5c\nres = Book.objects.select_related("publish").select_related("detail")<\/code><\/pre>\n
\uff082\uff09\u6df1\u5c42\u67e5\u8be2<\/h4>\n
\u5bf9\u4e8e\u8de8\u8d8a\u4e86n\u5f20\u8868\u7684\u6df1\u5c42\u67e5\u8be2\uff0c \u4f9d\u7136\u9700\u8981\u67e5\u8be2\u591a\u6b21\uff0c\u4f8b\u5982\u4e0b\u8ff0\u4ee3\u7801\u4f9d\u7136\u9700\u8981\u91cd\u590d\u67e5\u8be2\u4e24\u6b21<\/p>\n
article=models.Article.objects.select_related("blog").get(nid=1)\nprint(article.blog.user.username)  # \u9700\u8981\u91cd\u590d\u4e24\u6b21\u8fdb\u884c\u67e5\u8be2<\/code><\/pre>\n
\u8fd9\u662f\u56e0\u4e3a\u7b2c\u4e00\u6b21\u67e5\u8be2\u6ca1\u6709query\u5230userInfo\u8868\uff0c\u6240\u4ee5\uff0c\u4fee\u6539\u5982\u4e0b\uff1a<\/p>\n
article=models.Article.objects.select_related("blog__user").get(nid=1)\nprint(article.blog.user.username)<\/code><\/pre>\n
\uff083\uff09\u603b\u7ed3<\/h4>\n
l select_related\u4e3b\u8981\u9488\u4e00\u5bf9\u4e00\u548c\u591a\u5bf9\u4e00\u5173\u7cfb\u8fdb\u884c\u4f18\u5316\u3002<\/p>\n
l select_related\u4f7f\u7528SQL\u7684JOIN\u8bed\u53e5\u8fdb\u884c\u4f18\u5316\uff0c\u901a\u8fc7\u51cf\u5c11SQL\u67e5\u8be2\u7684\u6b21\u6570\u6765\u8fdb\u884c\u4f18\u5316\u3001\u63d0\u9ad8\u6027\u80fd\u3002<\/p>\n
l \u53ef\u4ee5\u901a\u8fc7\u53ef\u53d8\u957f\u53c2\u6570\u6307\u5b9a\u9700\u8981select_related\u7684\u5b57\u6bb5\u540d\u3002\u4e5f\u53ef\u4ee5\u901a\u8fc7\u4f7f\u7528\u53cc\u4e0b\u5212\u7ebf\u201c__\u201d\u8fde\u63a5\u5b57\u6bb5\u540d\u6765\u5b9e\u73b0\u6307\u5b9a\u7684\u9012\u5f52\u67e5\u8be2\u3002<\/p>\n
l \u6ca1\u6709\u6307\u5b9a\u7684\u5b57\u6bb5\u4e0d\u4f1a\u7f13\u5b58\uff0c\u6ca1\u6709\u6307\u5b9a\u7684\u6df1\u5ea6\u4e0d\u4f1a\u7f13\u5b58\uff0c\u5982\u679c\u8981\u8bbf\u95ee\u7684\u8bddDjango\u4f1a\u518d\u6b21\u8fdb\u884cSQL\u67e5\u8be2\u3002<\/p>\n
l \u4e5f\u53ef\u4ee5\u901a\u8fc7depth\u53c2\u6570\u6307\u5b9a\u9012\u5f52\u7684\u6df1\u5ea6\uff0cDjango\u4f1a\u81ea\u52a8\u7f13\u5b58\u6307\u5b9a\u6df1\u5ea6\u5185\u6240\u6709\u7684\u5b57\u6bb5\u3002\u5982\u679c\u8981\u8bbf\u95ee\u6307\u5b9a\u6df1\u5ea6\u5916\u7684\u5b57\u6bb5\uff0cDjango\u4f1a\u518d\u6b21\u8fdb\u884cSQL\u67e5\u8be2\u3002<\/p>\n
l \u4e5f\u63a5\u53d7\u65e0\u53c2\u6570\u7684\u8c03\u7528\uff0cDjango\u4f1a\u5c3d\u53ef\u80fd\u6df1\u7684\u9012\u5f52\u67e5\u8be2\u6240\u6709\u7684\u5b57\u6bb5\u3002\u4f46\u6ce8\u610f\u6709Django\u9012\u5f52\u7684\u9650\u5236\u548c\u6027\u80fd\u7684\u6d6a\u8d39\u3002<\/p>\n
l Django >= 1.7\uff0c\u94fe\u5f0f\u8c03\u7528\u7684select_related\u76f8\u5f53\u4e8e\u4f7f\u7528\u53ef\u53d8\u957f\u53c2\u6570\u3002Django < 1.7\uff0c\u94fe\u5f0f\u8c03\u7528\u4f1a\u5bfc\u81f4\u524d\u8fb9\u7684select_related\u5931\u6548\uff0c\u53ea\u4fdd\u7559\u6700\u540e\u4e00\u4e2a\u3002<\/p>\n
prefetch_related()<\/h4>\n
\u5bf9\u4e8e\u591a\u5bf9\u591a\u5b57\u6bb5\uff08ManyToManyField\uff09\u548c\u4e00\u5bf9\u591a\u5b57\u6bb5\uff0c\u53ef\u4ee5\u4f7f\u7528prefetch_related()\u6765\u8fdb\u884c\u4f18\u5316\uff0cprefetch_related()\u7684\u5e95\u5c42\u5c31\u662f\u5b50\u67e5\u8be2\uff0c\u5728\u4f7f\u7528\u65f6select_related\u4e0eprefetch_related\u662f\u6ca1\u6709\u5dee\u522b\u7684\uff0c\u4f46\u662f\u5e95\u5c42\u662f\u6709\u5dee\u522b\u7684<\/p>\n
\u9488\u5bf9\u4e00\u5bf9\u591a\u5b57\u6bb5<\/p>\n
# \u6548\u679c\u4e0eselect_related()\u4e00\u6837\nres = Book.objects.prefetch_related('publish')  \n\nfor obj in res:\n    print(obj.publish.name)\n\nfor obj in res:\n    print(obj.publish.city)<\/code><\/pre>\n
\u9488\u5bf9\u591a\u5bf9\u591a\u5b57\u6bb5<\/p>
<\/div>
\u67e5\u770b\u66f4\u591a<\/h2>
\u8054\u7cfb\u7ba1\u7406\u5458\u5fae\u4fe1tutu19192010\uff0c\u6ce8\u518c\u8d26\u53f7<\/p>\n<\/div>
<\/div>
<\/td><\/tr>
<\/td><\/tr><\/tbody><\/table>
<\/td><\/tr><\/tbody><\/table><\/form>
Register<\/a><\/div>
Forgotten username or password?<\/a><\/div>
<\/div><\/div><\/div>
<\/div>","protected":false},"excerpt":{"rendered":"
QuerySet\u5bf9\u8c61\u4e0e\u67e5\u8be2\u4f18\u5316 \u4e00\u3001QuerySet\u5bf9\u8c61 Django\u7684ORM\u4e2d\u5b58\u5728\u67e5\u8be2\u96c6\u7684\u6982\u5ff5\u3002 \u67e5\u8be2\u96c6\uff0c\u4e5f […]<\/p>\n","protected":false},"author":3,"featured_media":6776,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[3,405],"tags":[],"_links":{"self":[{"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/posts\/6167"}],"collection":[{"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/egonlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=6167"}],"version-history":[{"count":0,"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/posts\/6167\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/media\/6776"}],"wp:attachment":[{"href":"https:\/\/egonlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=6167"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/egonlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=6167"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/egonlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=6167"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}