{"id":21513,"date":"2024-01-02T10:38:25","date_gmt":"2024-01-02T10:38:25","guid":{"rendered":"https:\/\/server.hk\/blog\/21513\/"},"modified":"2024-11-14T10:31:31","modified_gmt":"2024-11-14T02:31:31","slug":"mongodb-glossary-projection","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/21513\/","title":{"rendered":"MongoDB \u8a5e\u5f59\u8868 &#8211; \u6295\u5f71"},"content":{"rendered":"<p>================================<\/p>\n<h1 id=\"mongodb-glossary-projection-MivELiFMVz\">MongoDB \u8a5e\u5f59\u8868 &#8211; \u6295\u5f71<\/h1>\n<p>\u5728 MongoDB \u7684\u4e16\u754c\u4e2d\uff0c\u6295\u5f71\u6307\u7684\u662f\u5f9e\u6587\u4ef6\u6216\u591a\u500b\u6587\u4ef6\u96c6\u5408\u4e2d\u9078\u64c7\u7279\u5b9a\u6b04\u4f4d\u7684\u904e\u7a0b\u3002\u9019\u4f7f\u60a8\u80fd\u5920\u53ea\u6aa2\u7d22\u6240\u9700\u7684\u6578\u64da\uff0c\u5f9e\u800c\u6e1b\u5c11\u7db2\u7d61\u8ca0\u64d4\u4e26\u63d0\u5347\u67e5\u8a62\u6548\u80fd\u3002\u5728\u672c\u6587\u4e2d\uff0c\u6211\u5011\u5c07\u63a2\u8a0e MongoDB \u4e2d\u7684\u6295\u5f71\u6982\u5ff5\uff0c\u4ee5\u53ca\u5982\u4f55\u6709\u6548\u5730\u904b\u7528\u5b83\u3002<\/p>\n<h2 id=\"understanding-projection-MivELiFMVz\">\u7406\u89e3\u6295\u5f71<\/h2>\n<p>\u7576\u67e5\u8a62 MongoDB \u6578\u64da\u5eab\u6642\uff0c\u60a8\u4e0d\u4e00\u5b9a\u9700\u8981\u6aa2\u7d22\u6587\u4ef6\u4e2d\u7684\u6240\u6709\u6b04\u4f4d\u3002\u5728\u8a31\u591a\u60c5\u6cc1\u4e0b\uff0c\u60a8\u53ea\u9700\u8981\u5176\u4e2d\u7684\u4e00\u90e8\u5206\u6578\u64da\u3002\u9019\u6642\uff0c\u6295\u5f71\u5c31\u80fd\u6d3e\u4e0a\u7528\u5834\u3002\u6295\u5f71\u5141\u8a31\u60a8\u6307\u5b9a\u5728\u67e5\u8a62\u7d50\u679c\u4e2d\u8981\u5305\u62ec\u6216\u6392\u9664\u7684\u6b04\u4f4d\u3002<\/p>\n<p>\u9ed8\u8a8d\u60c5\u6cc1\u4e0b\uff0c\u7576\u60a8\u5728 MongoDB \u4e2d\u57f7\u884c\u67e5\u8a62\u6642\uff0c\u5b83\u6703\u8fd4\u56de\u5339\u914d\u6587\u4ef6\u7684\u6240\u6709\u6b04\u4f4d\u3002\u7136\u800c\uff0c\u901a\u904e\u4f7f\u7528\u6295\u5f71\uff0c\u60a8\u53ef\u4ee5\u9650\u5236\u8fd4\u56de\u7684\u6b04\u4f4d\uff0c\u50c5\u9650\u65bc\u8207\u60a8\u7684\u61c9\u7528\u7a0b\u5f0f\u6216\u67e5\u8a62\u76f8\u95dc\u7684\u6b04\u4f4d\u3002<\/p>\n<h2 id=\"projection-syntax-MivELiFMVz\">\u6295\u5f71\u8a9e\u6cd5<\/h2>\n<p>MongoDB \u4e2d\u7684\u6295\u5f71\u8a9e\u6cd5\u76f8\u7576\u7c21\u55ae\u3002\u8981\u5305\u62ec\u7279\u5b9a\u6b04\u4f4d\uff0c\u60a8\u53ef\u4ee5\u4f7f\u7528 <code>1<\/code> \u503c\uff0c\u800c\u8981\u6392\u9664\u6b04\u4f4d\uff0c\u5247\u4f7f\u7528 <code>0<\/code> \u503c\u3002\u4ee5\u4e0b\u662f\u7bc4\u4f8b\uff1a<\/p>\n<pre>\r\ndb.collection.find({}, { field1: 1, field2: 1, _id: 0 })\r\n<\/pre>\n<p>\u5728\u4e0a\u8ff0\u7bc4\u4f8b\u4e2d\uff0c\u6211\u5011\u67e5\u8a62\u4e86 <code>collection<\/code>\uff0c\u4e26\u6307\u5b9a\u6211\u5011\u60f3\u8981\u5305\u62ec <code>field1<\/code> \u548c <code>field2<\/code>\uff0c\u540c\u6642\u6392\u9664 <code>_id<\/code> \u6b04\u4f4d\u3002<\/p>\n<p>\u60a8\u4e5f\u53ef\u4ee5\u4f7f\u7528\u6295\u5f71\u4f86\u5305\u62ec\u6216\u6392\u9664\u5d4c\u5957\u6587\u4ef6\u6216\u6578\u7d44\u4e2d\u7684\u6b04\u4f4d\u3002\u4f8b\u5982\uff1a<\/p>\n<pre>\r\ndb.collection.find({}, { \"nested.field1\": 1, \"arrayField.$\": 1, _id: 0 })\r\n<\/pre>\n<p>\u5728\u6b64\u7bc4\u4f8b\u4e2d\uff0c\u6211\u5011\u5305\u62ec\u4e86\u5d4c\u5957\u6587\u4ef6\u4e2d\u7684 <code>field1<\/code>\uff0c\u4ee5\u53ca\u6578\u7d44 <code>arrayField<\/code> \u7684\u7b2c\u4e00\u500b\u5143\u7d20\u3002<\/p>\n<h2 id=\"projection-operators-MivELiFMVz\">\u6295\u5f71\u904b\u7b97\u7b26<\/h2>\n<p>MongoDB \u63d0\u4f9b\u4e86\u5e7e\u500b\u6295\u5f71\u904b\u7b97\u7b26\uff0c\u5141\u8a31\u60a8\u64cd\u4f5c\u6295\u5f71\u7684\u6b04\u4f4d\u3002\u4e00\u4e9b\u5e38\u7528\u7684\u904b\u7b97\u7b26\u5305\u62ec\uff1a<\/p>\n<ul>\n<li><code>$elemMatch<\/code>\uff1a\u53ea\u9078\u64c7\u6578\u7d44\u4e2d\u7b2c\u4e00\u500b\u5339\u914d\u6307\u5b9a\u689d\u4ef6\u7684\u5143\u7d20\u3002<\/li>\n<li><code>$slice<\/code>\uff1a\u9650\u5236\u6578\u7d44\u6b04\u4f4d\u4e2d\u8fd4\u56de\u7684\u5143\u7d20\u6578\u91cf\u3002<\/li>\n<li><code>$meta<\/code>\uff1a\u8fd4\u56de\u8207\u6587\u672c\u641c\u7d22\u5206\u6578\u76f8\u95dc\u7684\u5143\u6578\u64da\u3002<\/li>\n<\/ul>\n<p>\u9019\u4e9b\u904b\u7b97\u7b26\u70ba\u6839\u64da\u60a8\u7684\u5177\u9ad4\u9700\u6c42\u8abf\u6574\u67e5\u8a62\u8f38\u51fa\u63d0\u4f9b\u4e86\u5f37\u5927\u7684\u80fd\u529b\u3002<\/p>\n<h2 id=\"benefits-of-projection-MivELiFMVz\">\u6295\u5f71\u7684\u512a\u9ede<\/h2>\n<p>\u5728 MongoDB \u67e5\u8a62\u4e2d\u4f7f\u7528\u6295\u5f71\u5177\u6709\u591a\u9805\u512a\u9ede\uff1a<\/p>\n<ul>\n<li><strong>\u63d0\u5347\u6548\u80fd\uff1a<\/strong>\u901a\u904e\u53ea\u6aa2\u7d22\u5fc5\u8981\u7684\u6b04\u4f4d\uff0c\u6295\u5f71\u6e1b\u5c11\u4e86\u50b3\u8f38\u5230\u7db2\u7d61\u4e0a\u7684\u6578\u64da\u91cf\uff0c\u5f9e\u800c\u52a0\u5feb\u4e86\u67e5\u8a62\u57f7\u884c\u901f\u5ea6\u3002<\/li>\n<li><strong>\u6e1b\u5c11\u7db2\u7d61\u8ca0\u64d4\uff1a<\/strong>\u901a\u904e\u6295\u5f71\uff0c\u60a8\u53ef\u4ee5\u5c07 MongoDB \u670d\u52d9\u5668\u8207\u60a8\u7684\u61c9\u7528\u7a0b\u5f0f\u4e4b\u9593\u50b3\u8f38\u7684\u6578\u64da\u91cf\u964d\u81f3\u6700\u5c11\uff0c\u5f9e\u800c\u63d0\u5347\u7db2\u7d61\u6548\u80fd\u3002<\/li>\n<li><strong>\u6578\u64da\u96b1\u79c1\uff1a<\/strong>\u6295\u5f71\u5141\u8a31\u60a8\u5f9e\u67e5\u8a62\u7d50\u679c\u4e2d\u6392\u9664\u654f\u611f\u6216\u4e0d\u5fc5\u8981\u7684\u6b04\u4f4d\uff0c\u78ba\u4fdd\u6578\u64da\u96b1\u79c1\u8207\u5b89\u5168\u3002<\/li>\n<\/ul>\n<h2 id=\"conclusion-MivELiFMVz\">\u7e3d\u7d50<\/h2>\n<p>\u6295\u5f71\u662f MongoDB \u4e2d\u4e00\u500b\u5f37\u5927\u7684\u529f\u80fd\uff0c\u5141\u8a31\u60a8\u63a7\u5236\u67e5\u8a62\u7d50\u679c\u4e2d\u8fd4\u56de\u7684\u6b04\u4f4d\u3002\u901a\u904e\u6307\u5b9a\u8981\u5305\u62ec\u6216\u6392\u9664\u7684\u6b04\u4f4d\uff0c\u60a8\u53ef\u4ee5\u512a\u5316\u67e5\u8a62\u6548\u80fd\u3001\u6e1b\u5c11\u7db2\u7d61\u8ca0\u64d4\u4e26\u63d0\u5347\u6578\u64da\u96b1\u79c1\u3002\u7406\u89e3\u4e26\u6709\u6548\u904b\u7528\u6295\u5f71\u53ef\u4ee5\u5927\u5927\u63d0\u5347 MongoDB \u67e5\u8a62\u7684\u6548\u7387\u8207\u6548\u679c\u3002<\/p>\n<p>\u5982\u9700\u4e86\u89e3\u66f4\u591a\u6709\u95dc MongoDB \u53ca\u5176\u529f\u80fd\uff0c\u60a8\u53ef\u4ee5\u8003\u616e\u63a2\u7d22 <a href=\"https:\/\/server.hk\">Server.HK<\/a>\uff0c\u9019\u662f\u4e00\u5bb6\u9818\u5148\u7684 VPS \u8a17\u7ba1\u516c\u53f8\uff0c\u63d0\u4f9b\u53ef\u9760\u4e14\u9ad8\u6548\u80fd\u7684\u8a17\u7ba1\u89e3\u6c7a\u65b9\u6848\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>================&#46;&#46;&#46;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4925],"tags":[],"class_list":["post-21513","post","type-post","status-publish","format-standard","hentry","category-4925"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/21513","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=21513"}],"version-history":[{"count":2,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/21513\/revisions"}],"predecessor-version":[{"id":23950,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/21513\/revisions\/23950"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=21513"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=21513"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=21513"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}