{"id":29806,"date":"2023-10-19T05:42:43","date_gmt":"2023-12-11T08:35:35","guid":{"rendered":"https:\/\/www.silicloud.com\/zh\/blog\/%e6%95%b4%e7%90%86-mongodb-mongoid-%e4%b8%ad%e7%9a%84-exists-%e5%8a%9f%e8%83%bd%e3%80%82\/"},"modified":"2025-08-12T16:00:28","modified_gmt":"2025-08-12T08:00:28","slug":"%e6%95%b4%e7%90%86-mongodb-mongoid-%e4%b8%ad%e7%9a%84-exists-%e5%8a%9f%e8%83%bd%e3%80%82","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/zh\/blog\/%e6%95%b4%e7%90%86-mongodb-mongoid-%e4%b8%ad%e7%9a%84-exists-%e5%8a%9f%e8%83%bd%e3%80%82\/","title":{"rendered":"\u6574\u7406 MongoDB\/Mongoid \u4e2d\u7684 exists \u529f\u80fd"},"content":{"rendered":"

MongoDB \u7684 $exists \u7684\u884c\u4e3a\u662f\u4ec0\u4e48\uff1f\u5047\u8bbe\u6709\u4ee5\u4e0b\u6570\u636e\u3002<\/p>\n
><\/span> db<\/span>.<\/span>items<\/span>.<\/span>find<\/span>()<\/span>\r\n{<\/span> \"<\/span>_id<\/span>\"<\/span> :<\/span> ObjectId<\/span>(<\/span>\"<\/span>5de50feab2e406088d483c44<\/span>\"<\/span>),<\/span> \"<\/span>name<\/span>\"<\/span> :<\/span> \"<\/span>item01<\/span>\"<\/span>,<\/span> \"<\/span>color<\/span>\"<\/span> :<\/span> \"<\/span>red<\/span>\"<\/span>,<\/span> \"<\/span>size<\/span>\"<\/span> :<\/span> \"<\/span>M<\/span>\"<\/span> }<\/span>\r\n{<\/span> \"<\/span>_id<\/span>\"<\/span> :<\/span> ObjectId<\/span>(<\/span>\"<\/span>5de51001b2e406088d483c45<\/span>\"<\/span>),<\/span> \"<\/span>name<\/span>\"<\/span> :<\/span> \"<\/span>item02<\/span>\"<\/span>,<\/span> \"<\/span>color<\/span>\"<\/span> :<\/span> \"<\/span>blue<\/span>\"<\/span>,<\/span> \"<\/span>size<\/span>\"<\/span> :<\/span> \"<\/span>S<\/span>\"<\/span>,<\/span> \"<\/span>memo<\/span>\"<\/span> :<\/span> null<\/span> }<\/span>\r\n{<\/span> \"<\/span>_id<\/span>\"<\/span> :<\/span> ObjectId<\/span>(<\/span>\"<\/span>5de51012b2e406088d483c46<\/span>\"<\/span>),<\/span> \"<\/span>name<\/span>\"<\/span> :<\/span> \"<\/span>item03<\/span>\"<\/span>,<\/span> \"<\/span>color<\/span>\"<\/span> :<\/span> \"<\/span>yellow<\/span>\"<\/span>,<\/span> \"<\/span>size<\/span>\"<\/span> :<\/span> \"<\/span>L<\/span>\"<\/span>,<\/span> \"<\/span>memo<\/span>\"<\/span> :<\/span> \"\"<\/span> }<\/span>\r\n{<\/span> \"<\/span>_id<\/span>\"<\/span> :<\/span> ObjectId<\/span>(<\/span>\"<\/span>5de51029b2e406088d483c47<\/span>\"<\/span>),<\/span> \"<\/span>name<\/span>\"<\/span> :<\/span> \"<\/span>item04<\/span>\"<\/span>,<\/span> \"<\/span>color<\/span>\"<\/span> :<\/span> \"<\/span>green<\/span>\"<\/span>,<\/span> \"<\/span>size<\/span>\"<\/span> :<\/span> \"<\/span>M<\/span>\"<\/span>,<\/span> \"<\/span>memo<\/span>\"<\/span> :<\/span> \"<\/span>hoge<\/span>\"<\/span> }<\/span>\r\n<\/code><\/pre>\n
\u4f7f\u7528$exists\u6765\u83b7\u53d6\u4ec5\u5305\u542b\u5907\u5fd8\u5f55\u6570\u636e\u7684\u60c5\u51b5\u5982\u4e0b\u3002<\/p>\n
><\/span> db<\/span>.<\/span>items<\/span>.<\/span>find<\/span>({<\/span>memo<\/span>:<\/span> {<\/span>$exists<\/span>:<\/span> true<\/span>}})<\/span>\r\n{<\/span> \"<\/span>_id<\/span>\"<\/span> :<\/span> ObjectId<\/span>(<\/span>\"<\/span>5de51001b2e406088d483c45<\/span>\"<\/span>),<\/span> \"<\/span>name<\/span>\"<\/span> :<\/span> \"<\/span>item02<\/span>\"<\/span>,<\/span> \"<\/span>color<\/span>\"<\/span> :<\/span> \"<\/span>blue<\/span>\"<\/span>,<\/span> \"<\/span>size<\/span>\"<\/span> :<\/span> \"<\/span>S<\/span>\"<\/span>,<\/span> \"<\/span>memo<\/span>\"<\/span> :<\/span> null<\/span> }<\/span>\r\n{<\/span> \"<\/span>_id<\/span>\"<\/span> :<\/span> ObjectId<\/span>(<\/span>\"<\/span>5de51012b2e406088d483c46<\/span>\"<\/span>),<\/span> \"<\/span>name<\/span>\"<\/span> :<\/span> \"<\/span>item03<\/span>\"<\/span>,<\/span> \"<\/span>color<\/span>\"<\/span> :<\/span> \"<\/span>yellow<\/span>\"<\/span>,<\/span> \"<\/span>size<\/span>\"<\/span> :<\/span> \"<\/span>L<\/span>\"<\/span>,<\/span> \"<\/span>memo<\/span>\"<\/span> :<\/span> \"\"<\/span> }<\/span>\r\n{<\/span> \"<\/span>_id<\/span>\"<\/span> :<\/span> ObjectId<\/span>(<\/span>\"<\/span>5de51029b2e406088d483c47<\/span>\"<\/span>),<\/span> \"<\/span>name<\/span>\"<\/span> :<\/span> \"<\/span>item04<\/span>\"<\/span>,<\/span> \"<\/span>color<\/span>\"<\/span> :<\/span> \"<\/span>green<\/span>\"<\/span>,<\/span> \"<\/span>size<\/span>\"<\/span> :<\/span> \"<\/span>M<\/span>\"<\/span>,<\/span> \"<\/span>memo<\/span>\"<\/span> :<\/span> \"<\/span>hoge<\/span>\"<\/span> }<\/span>\r\n<\/code><\/pre>\n
$exists \u53ea\u8bc4\u4f30\u76ee\u6807\u5b57\u6bb5\u662f\u5426\u5b58\u5728\u3002
\n\u56e0\u6b64\uff0c\u65e0\u8bba memo \u5b57\u6bb5\u7684\u503c\u662f null \u8fd8\u662f\u7a7a\uff0c$exists \u90fd\u88ab\u89c6\u4e3a true\u3002<\/p>\n
\u5230\u76ee\u524d\u4e3a\u6b62\uff0c\u6211\u4eec\u5728\u8ba8\u8bba MongoDB \u7684 $exists\uff0c\u5e76\u6ca1\u6709\u4ec0\u4e48\u96be\u7684\u3002<\/p>\n
Mongoid \u7684 exists \u884c\u4e3a
\nMongoid \u662f\u7528\u4e8e\u5728 Ruby \u4e0a\u64cd\u4f5c MongoDB \u7684\u5bf9\u8c61\u6587\u6863\u6620\u5c04\uff08ODM\uff09\u5de5\u5177\u3002
\n\u5f53\u7136\uff0cMongoid \u4e5f\u5b58\u5728\u4e0e MongoDB \u7684 $exists \u76f8\u5bf9\u5e94\u7684\u529f\u80fd\u3002<\/p>\n
\u9996\u5148\uff0c\u6211\u4eec\u5b9a\u4e49\u4e00\u4e2a\u7c7b\u5982\u4e0b\u3002<\/p>\n
class<\/span> Item<\/span>\r\n  include<\/span> Mongoid<\/span>::<\/span>Document<\/span>\r\n\r\n  field<\/span> :name<\/span>\r\n  field<\/span> :color<\/span>\r\n  field<\/span> :size<\/span>\r\n  field<\/span> :memo<\/span>\r\nend<\/span>\r\n<\/code><\/pre>\n
\u53ea\u9700\u6267\u884c\u4ee5\u4e0b\u4ee3\u7801\u5373\u53ef\u83b7\u53d6\u6240\u6709\u8bb0\u5f55\u3002
\n\uff08\u5728\u8fd9\u91cc\uff0c\u4f7f\u7528\u4e86Rails\u63a7\u5236\u53f0\uff09<\/p>\n
irb<\/span>(<\/span>main<\/span>):<\/span>001<\/span>:<\/span>0<\/span>><\/span> Item<\/span>.<\/span>each<\/span> {<\/span> |<\/span>i<\/span>|<\/span> p<\/span> \"<\/span>#{<\/span>i<\/span>.<\/span>_id<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>name<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>color<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>size<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>memo<\/span>}<\/span>\"<\/span> };<\/span> nil<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>1<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> #1 | sandbox.find | STARTED | {\"find\"=>\"items\", \"filter\"=>{}, \"lsid\"=>{\"id\"=><BSON::Binary:0x70346640265920 type=uuid data=0x672fb96b60a9434f...>}}<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>1<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> |<\/span> sandbox<\/span>.<\/span>find<\/span> |<\/span> SUCCEEDED<\/span> |<\/span> 0.002<\/span>s<\/span>\r\n\"5de50feab2e406088d483c44, item01, red, M, \"<\/span>\r\n\"5de51001b2e406088d483c45, item02, blue, S, \"<\/span>\r\n\"5de51012b2e406088d483c46, item03, yellow, L, \"<\/span>\r\n\"5de51029b2e406088d483c47, item04, green, M, hoge\"<\/span>\r\n=><\/span> nil<\/span>\r\n<\/code><\/pre>\n
\u4f7f\u7528exists\u5173\u952e\u5b57\uff0c\u5373\u53ef\u5f97\u5230\u4ee5\u4e0b\u7ed3\u679c\u3002<\/p>\n
irb<\/span>(<\/span>main<\/span>):<\/span>002<\/span>:<\/span>0<\/span>><\/span> Item<\/span>.<\/span>exists<\/span>(<\/span>memo: <\/span>true<\/span>).<\/span>each<\/span> {<\/span> |<\/span>i<\/span>|<\/span> p<\/span> \"<\/span>#{<\/span>i<\/span>.<\/span>_id<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>name<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>color<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>size<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>memo<\/span>}<\/span>\"<\/span> };<\/span> nil<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>2<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> #1 | sandbox.find | STARTED | {\"find\"=>\"items\", \"filter\"=>{\"memo\"=>{\"$exists\"=>true}}, \"lsid\"=>{\"id\"=><BSON::Binary:0x70346640265920 type=uuid data=0x672fb96b60a9434f...>}}<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>2<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> |<\/span> sandbox<\/span>.<\/span>find<\/span> |<\/span> SUCCEEDED<\/span> |<\/span> 0.002<\/span>s<\/span>\r\n\"5de51001b2e406088d483c45, item02, blue, S, \"<\/span>\r\n\"5de51012b2e406088d483c46, item03, yellow, L, \"<\/span>\r\n\"5de51029b2e406088d483c47, item04, green, M, hoge\"<\/span>\r\n=><\/span> nil<\/span>\r\n<\/code><\/pre>\n
\u53ef\u4ee5\u7528 Item.where(:memo.exists => true) \u6765\u4ee3\u66ff Item.exists(memo: true)\u3002<\/p>\n
\u5230\u76ee\u524d\u4e3a\u6b62\uff0c\u4e0eMongoDB\u7684$exists\u5177\u6709\u76f8\u540c\u7684\u884c\u4e3a\u3002<\/p>\n
\u5982\u679c\u5728Mongoid\u4e2d\u8bbe\u7f6e\u4e86\u9ed8\u8ba4\u503c\uff0c\u5176\u884c\u4e3a\u662f\u600e\u6837\u7684\uff1f
\n\u5728\u6a21\u578b\u4e2d\uff0c\u53ef\u4ee5\u4e3amemo\u5b57\u6bb5\u8bbe\u7f6e\u9ed8\u8ba4\u503c\u3002<\/p>\n
class<\/span> Item<\/span>\r\n  include<\/span> Mongoid<\/span>::<\/span>Document<\/span>\r\n\r\n  field<\/span> :name<\/span>\r\n  field<\/span> :color<\/span>\r\n  field<\/span> :size<\/span>\r\n  field<\/span> :memo<\/span>,<\/span> default: <\/span>'empty'<\/span>\r\nend<\/span>\r\n<\/code><\/pre>\n
\u5728Rails\u63a7\u5236\u53f0\u4e0a\u8fdb\u884c\u91cd\u65b0\u52a0\u8f7d\u4ee5\u52a0\u8f7d\u6a21\u578b\u7684\u66f4\u6539\u3002<\/p>\n
irb<\/span>(<\/span>main<\/span>):<\/span>003<\/span>:<\/span>0<\/span>><\/span> reload!<\/span>\r\nReloading<\/span>...<\/span>\r\n=><\/span> true<\/span>\r\n<\/code><\/pre>\n
\u5982\u679c\u5168\u90e8\u83b7\u5f97\uff0c\u4f1a\u53d8\u6210\u4ee5\u4e0b\u8fd9\u6837\u3002<\/p>\n
irb<\/span>(<\/span>main<\/span>):<\/span>004<\/span>:<\/span>0<\/span>><\/span> Item<\/span>.<\/span>each<\/span> {<\/span> |<\/span>i<\/span>|<\/span> p<\/span> \"<\/span>#{<\/span>i<\/span>.<\/span>_id<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>name<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>color<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>size<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>memo<\/span>}<\/span>\"<\/span> };<\/span> nil<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>3<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> #1 | sandbox.find | STARTED | {\"find\"=>\"items\", \"filter\"=>{}, \"lsid\"=>{\"id\"=><BSON::Binary:0x70346640265920 type=uuid data=0x672fb96b60a9434f...>}}<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>3<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> |<\/span> sandbox<\/span>.<\/span>find<\/span> |<\/span> SUCCEEDED<\/span> |<\/span> 0.002<\/span>s<\/span>\r\n\"5de50feab2e406088d483c44, item01, red, M, empty\"<\/span>\r\n\"5de51001b2e406088d483c45, item02, blue, S, \"<\/span>\r\n\"5de51012b2e406088d483c46, item03, yellow, L, \"<\/span>\r\n\"5de51029b2e406088d483c47, item04, green, M, hoge\"<\/span>\r\n=><\/span> nil<\/span>\r\n<\/code><\/pre>\n
\u53ef\u4ee5\u770b\u5230\uff0citem01\u7684\u5907\u5fd8\u5f55\u5df2\u7ecf\u8bbe\u7f6e\u4e86\u9ed8\u8ba4\u503c\u3002<\/p>\n
\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u5982\u679c\u50cf\u4e4b\u524d\u90a3\u6837\u4f7f\u7528exists\u8fdb\u884c\u7b5b\u9009\uff0c\u7ed3\u679c\u5982\u4e0b\u3002<\/p>\n
irb<\/span>(<\/span>main<\/span>):<\/span>005<\/span>:<\/span>0<\/span>><\/span> Item<\/span>.<\/span>exists<\/span>(<\/span>memo: <\/span>true<\/span>).<\/span>each<\/span> {<\/span> |<\/span>i<\/span>|<\/span> p<\/span> \"<\/span>#{<\/span>i<\/span>.<\/span>_id<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>name<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>color<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>size<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>memo<\/span>}<\/span>\"<\/span> };<\/span> nil<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>4<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> #1 | sandbox.find | STARTED | {\"find\"=>\"items\", \"filter\"=>{\"memo\"=>{\"$exists\"=>true}}, \"lsid\"=>{\"id\"=><BSON::Binary:0x70346640265920 type=uuid data=0x672fb96b60a9434f...>}}<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>4<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> |<\/span> sandbox<\/span>.<\/span>find<\/span> |<\/span> SUCCEEDED<\/span> |<\/span> 0.002<\/span>s<\/span>\r\n\"5de51001b2e406088d483c45, item02, blue, S, \"<\/span>\r\n\"5de51012b2e406088d483c46, item03, yellow, L, \"<\/span>\r\n\"5de51029b2e406088d483c47, item04, green, M, hoge\"<\/span>\r\n=><\/span> nil<\/span>\r\n<\/code><\/pre>\n
\u7269\u54c101\u6ca1\u6709\u88ab\u8f93\u51fa\u3002
\n\u6362\u53e5\u8bdd\u8bf4\uff0c\u5b58\u5728\u4e0e\u5426\u5e76\u4e0d\u5f71\u54cd\u9ed8\u8ba4\u503c\u7684\u7ed3\u679c\u3002
\n\u9ed8\u8ba4\u503c\u53ea\u662f\u7528\u6765\u5728\u5e94\u7528\u7a0b\u5e8f\u4e2d\u8bbe\u7f6e\u5f53\u5b57\u6bb5\u4e0d\u5b58\u5728\u65f6\u8981\u5904\u7406\u7684\u503c\u3002
\n\u501f\u52a9\u8fd9\u4e00\u70b9\uff0c\u5e94\u7528\u7a0b\u5e8f\u53ef\u4ee5\u533a\u5206\u8be5\u503c\u662f\u9ed8\u8ba4\u503c\u8fd8\u662f\u5df2\u8bbe\u7f6e\u7684\u503c\u3002<\/p>\n
\u6dfb\u52a0\u4e00\u4e2a\u9879\u76ee\u3002<\/p>\n
><\/span> db<\/span>.<\/span>items<\/span>.<\/span>insert<\/span>({<\/span>name<\/span>:<\/span> '<\/span>item05<\/span>'<\/span>,<\/span> color<\/span>:<\/span> '<\/span>orange<\/span>'<\/span>,<\/span> size<\/span>:<\/span> '<\/span>S<\/span>'<\/span>,<\/span> memo<\/span>:<\/span> '<\/span>empty<\/span>'<\/span>})<\/span>\r\nWriteResult<\/span>({<\/span> \"<\/span>nInserted<\/span>\"<\/span> :<\/span> 1<\/span> })<\/span>\r\n<\/code><\/pre>\n
\u4f7f\u7528Rails\u63a7\u5236\u53f0\u8fdb\u884c\u5168\u8bb0\u5f55\u83b7\u53d6\u4f1a\u5982\u4e0b\u6240\u793a\u3002<\/p>\n
irb<\/span>(<\/span>main<\/span>):<\/span>006<\/span>:<\/span>0<\/span>><\/span> Item<\/span>.<\/span>each<\/span> {<\/span> |<\/span>i<\/span>|<\/span> p<\/span> \"<\/span>#{<\/span>i<\/span>.<\/span>_id<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>name<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>color<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>size<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>memo<\/span>}<\/span>\"<\/span> };<\/span> nil<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>5<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> #1 | sandbox.find | STARTED | {\"find\"=>\"items\", \"filter\"=>{}, \"lsid\"=>{\"id\"=><BSON::Binary:0x70346640265920 type=uuid data=0x672fb96b60a9434f...>}}<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>5<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> |<\/span> sandbox<\/span>.<\/span>find<\/span> |<\/span> SUCCEEDED<\/span> |<\/span> 0.002<\/span>s<\/span>\r\n\"5de50feab2e406088d483c44, item01, red, M, empty\"<\/span>\r\n\"5de51001b2e406088d483c45, item02, blue, S, \"<\/span>\r\n\"5de51012b2e406088d483c46, item03, yellow, L, \"<\/span>\r\n\"5de51029b2e406088d483c47, item04, green, M, hoge\"<\/span>\r\n\"5de51b39b2e406088d483c4a, item05, orange, S, empty\"<\/span>\r\n=><\/span> nil<\/span>\r\n<\/code><\/pre>\n
\u4ece\u8fd9\u4e2a\u7ed3\u679c\u6765\u770b\uff0c\u6211\u4eec\u65e0\u6cd5\u5206\u8fa8item01\u7684memo\u548citem05\u7684memo\u662f\u5426\u76f8\u540c\u3002<\/p>\n
irb<\/span>(<\/span>main<\/span>):<\/span>007<\/span>:<\/span>0<\/span>><\/span> Item<\/span>.<\/span>find_by<\/span>(<\/span>name: <\/span>'item01'<\/span>).<\/span>memo<\/span> ==<\/span> Item<\/span>.<\/span>find_by<\/span>(<\/span>name: <\/span>'item05'<\/span>).<\/span>memo<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>6<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> #1 | sandbox.find | STARTED | {\"find\"=>\"items\", \"filter\"=>{\"name\"=>\"item01\"}, \"lsid\"=>{\"id\"=><BSON::Binary:0x70346640265920 type=uuid data=0x672fb96b60a9434f...>}}<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>6<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> |<\/span> sandbox<\/span>.<\/span>find<\/span> |<\/span> SUCCEEDED<\/span> |<\/span> 0.002<\/span>s<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>7<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> #1 | sandbox.find | STARTED | {\"find\"=>\"items\", \"filter\"=>{\"name\"=>\"item05\"}, \"lsid\"=>{\"id\"=><BSON::Binary:0x70346640265920 type=uuid data=0x672fb96b60a9434f...>}}<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>7<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> |<\/span> sandbox<\/span>.<\/span>find<\/span> |<\/span> SUCCEEDED<\/span> |<\/span> 0.001<\/span>s<\/span>\r\n=><\/span> true<\/span>\r\n<\/code><\/pre>\n
\u5982\u679c\u4f7f\u7528\u201c\u5b58\u5728\u201d\u8fd9\u4e2a\u8bcd\uff0c\u5c31\u53ef\u4ee5\u533a\u5206\u51fa\u6765\u3002<\/p>\n
irb<\/span>(<\/span>main<\/span>):<\/span>00<\/span>8<\/span>:<\/span>0<\/span>><\/span> Item<\/span>.<\/span>exists<\/span>(<\/span>memo: <\/span>true<\/span>).<\/span>each<\/span> {<\/span> |<\/span>i<\/span>|<\/span> p<\/span> \"<\/span>#{<\/span>i<\/span>.<\/span>_id<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>name<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>color<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>size<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>memo<\/span>}<\/span>\"<\/span> };<\/span> nil<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>8<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> #1 | sandbox.find | STARTED | {\"find\"=>\"items\", \"filter\"=>{\"memo\"=>{\"$exists\"=>true}}, \"lsid\"=>{\"id\"=><BSON::Binary:0x70346640265920 type=uuid data=0x672fb96b60a9434f...>}}<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>8<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> |<\/span> sandbox<\/span>.<\/span>find<\/span> |<\/span> SUCCEEDED<\/span> |<\/span> 0.002<\/span>s<\/span>\r\n\"5de51001b2e406088d483c45, item02, blue, S, \"<\/span>\r\n\"5de51012b2e406088d483c46, item03, yellow, L, \"<\/span>\r\n\"5de51029b2e406088d483c47, item04, green, M, hoge\"<\/span>\r\n\"5de51b39b2e406088d483c4a, item05, orange, S, empty\"<\/span>\r\n=><\/span> nil<\/span>\r\n<\/code><\/pre>\n
\u5982\u679c\u60f3\u8981\u9006\u8f6c\u5c40\u52bf\uff0c\u8bf7\u53c2\u8003\u4ee5\u4e0b\u65b9\u6cd5\u3002<\/p>\n
irb<\/span>(<\/span>main<\/span>):<\/span>00<\/span>9<\/span>:<\/span>0<\/span>><\/span> Item<\/span>.<\/span>exists<\/span>(<\/span>memo: <\/span>false<\/span>).<\/span>each<\/span> {<\/span> |<\/span>i<\/span>|<\/span> p<\/span> \"<\/span>#{<\/span>i<\/span>.<\/span>_id<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>name<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>color<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>size<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>memo<\/span>}<\/span>\"<\/span> };<\/span> nil<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>9<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> #1 | sandbox.find | STARTED | {\"find\"=>\"items\", \"filter\"=>{\"memo\"=>{\"$exists\"=>false}}, \"lsid\"=>{\"id\"=><BSON::Binary:0x70346640265920 type=uuid data=0x672fb96b60a9434f...>}}<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>9<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> |<\/span> sandbox<\/span>.<\/span>find<\/span> |<\/span> SUCCEEDED<\/span> |<\/span> 0.003<\/span>s<\/span>\r\n\"5de50feab2e406088d483c44, item01, red, M, empty\"<\/span>\r\n=><\/span> nil<\/span>\r\n<\/code><\/pre>\n
\u6216\u8005\uff0c\u53ef\u4ee5\u76f4\u63a5where\uff08memo\uff1a’empty’\uff09\u6765\u4ec5\u83b7\u53d6item05\u3002<\/p>\n
irb<\/span>(<\/span>main<\/span>):<\/span>010<\/span>:<\/span>0<\/span>><\/span> Item<\/span>.<\/span>where<\/span>(<\/span>memo: <\/span>'empty'<\/span>).<\/span>each<\/span> {<\/span> |<\/span>i<\/span>|<\/span> p<\/span> \"<\/span>#{<\/span>i<\/span>.<\/span>_id<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>name<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>color<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>size<\/span>}<\/span>, <\/span>#{<\/span>i<\/span>.<\/span>memo<\/span>}<\/span>\"<\/span> };<\/span> nil<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>10<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> #1 | sandbox.find | STARTED | {\"find\"=>\"items\", \"filter\"=>{\"memo\"=>\"empty\"}, \"lsid\"=>{\"id\"=><BSON::Binary:0x70346640265920 type=uuid data=0x672fb96b60a9434f...>}}<\/span>\r\nMONGODB<\/span> |<\/span> [<\/span>10<\/span>]<\/span> localhost<\/span>:<\/span>28001<\/span> |<\/span> sandbox<\/span>.<\/span>find<\/span> |<\/span> SUCCEEDED<\/span> |<\/span> 0.002<\/span>s<\/span>\r\n\"5de51b39b2e406088d483c4a, item05, orange, S, empty\"<\/span>\r\n=><\/span> nil<\/span>\r\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
MongoDB \u7684 $exists \u7684\u884c\u4e3a\u662f\u4ec0\u4e48\uff1f\u5047\u8bbe\u6709\u4ee5\u4e0b\u6570\u636e\u3002 > db.items.find()  […]<\/p>\n","protected":false},"author":11,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[227],"class_list":["post-29806","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-227"],"yoast_head":"\n\u6574\u7406 MongoDB\/Mongoid \u4e2d\u7684 exists \u529f\u80fd - Blog - Silicon Cloud<\/title>\n<meta name=\"description\" content=\"\u5173\u4e8e\u6574\u7406 MongoDB\/Mongoid \u4e2d\u7684 exists \u529f\u80fd\u7684\u6280\u672f\u6587\u7ae0\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.silicloud.com\/zh\/blog\/\u6574\u7406-mongodb-mongoid-\u4e2d\u7684-exists-\u529f\u80fd\u3002\/\" \/>\n<meta property=\"og:locale\" content=\"zh_CN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"\u6574\u7406 MongoDB\/Mongoid \u4e2d\u7684 exists \u529f\u80fd\" \/>\n<meta property=\"og:description\" content=\"\u5173\u4e8e\u6574\u7406 MongoDB\/Mongoid \u4e2d\u7684 exists \u529f\u80fd\u7684\u6280\u672f\u6587\u7ae0\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.silicloud.com\/zh\/blog\/\u6574\u7406-mongodb-mongoid-\u4e2d\u7684-exists-\u529f\u80fd\u3002\/\" \/>\n<meta property=\"og:site_name\" content=\"Blog - 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