的MongoDB - 返回基于结果的数量不同的查询条件

Question

我有这样一个文件 -

{ 
type: "One", 
details: "This is one", 
at: "some place, where one is relevant" 
} 

类似模式的其他文件可以有不同的“细节”同“型”，“在”等等。 可以有几个'类型'。

现在，我想写一个查询，以返回给我一些匹配某些'类型'（我可以使用limit和$in）的文档的某个数字（上限，也就是5），这可以省略'type'条件if结果包含少于5个文件。例如，如果我只允许“一”和“两”作为“类型”，并且使用5的限制，那么如果结果的数量少于5（比如2），它应该返回给我那些具有“一”和“二”作为它们的类型（即2个文档）和另外3个文档而没有查看它们的“类型”的文档。

我希望这是有道理的！

Answer 1

如果你不喜欢排序weight使用可以看我的选择是使用aggregate与引入额外场weight例如脚本拉升匹配文档，然后和限制总的结果：

db.test.aggregate({ 
    $project: { 
    type: 1, 
    details: 1, 
    at: 1, 
    weight: { 
     $cond: [ 
     { "$or": [ 
      {$eq: ["$type", "One"] }, 
      {$eq: ["$type", "Two"] } 
     ] }, 
     0, 1] } 
    } }, 
    {$sort: {weight: 1}}, 
    { $limit : 5 } 
); 

关于这个例子的注释。为了简单起见，我用几个等于$的元素替换$ in。如果您不想在最终结果中包含weight，则可以通过在聚合管道中应用另一个投影来将其删除。

测试分贝：

> db.test.find({}) 
{ "_id" : ObjectId("58067329a7518db4d3d2e973"), "type" : "One", "details" : "This is one", "at" : "some place, where one is relevant" } 
{ "_id" : ObjectId("5806733da7518db4d3d2e974"), "type" : "Two", "details" : "This is two", "at" : "some place, where one is relevant" } 
{ "_id" : ObjectId("5806734ba7518db4d3d2e975"), "type" : "Three", "details" : "This is three", "at" : "some place, where one is relevant" } 
{ "_id" : ObjectId("58067374a7518db4d3d2e976"), "type" : "Four", "details" : "This is four", "at" : "some place, where one is relevant" } 
{ "_id" : ObjectId("58067381a7518db4d3d2e977"), "type" : "Five", "details" : "This is five", "at" : "some place, where one is relevant" } 
{ "_id" : ObjectId("5806738fa7518db4d3d2e978"), "type" : "Six", "details" : "This is six", "at" : "some place, where one is relevant" } 
{ "_id" : ObjectId("580673cfa7518db4d3d2e979"), "type" : "Seven", "details" : "This is seven", "at" : "some place, where one is relevant" }  

结果：

> db.test.aggregate({ $project: { type: 1, details: 1, at: 1, weight: { $cond: [ { "$or": [ {$eq: ["$type", "One"] }, {$eq: ["$type", "Two"] } ] }, 0, 1] } } }, {$sort: {weight: 1}}, { $limit : 5 }, {$project: {type: 1, details: 1, at: 1} }); 
{ "_id" : ObjectId("58067329a7518db4d3d2e973"), "type" : "One", "details" : "This is one", "at" : "some place, where one is relevant" } 
{ "_id" : ObjectId("5806733da7518db4d3d2e974"), "type" : "Two", "details" : "This is two", "at" : "some place, where one is relevant" } 
{ "_id" : ObjectId("58067374a7518db4d3d2e976"), "type" : "Four", "details" : "This is four", "at" : "some place, where one is relevant" } 
{ "_id" : ObjectId("58067381a7518db4d3d2e977"), "type" : "Five", "details" : "This is five", "at" : "some place, where one is relevant" } 
{ "_id" : ObjectId("5806734ba7518db4d3d2e975"), "type" : "Three", "details" : "This is three", "at" : "some place, where one is relevant" }