如何在mongodb中通过标签有条件地查找项目

Question

I am new to NoSQL and MongoDB and I am a little puzzled on what type of queries I can do and how to do them. my knowledge is limited to simpler queries

I would like to make what I think its a complicated query within MongoDB instead of using PHP to sort it but I do not know if it is possible or how to do it.

I have a tag field within my collection that is an array . {tag: ["blue","red","yellow","green","violet"]} .

First level problem: Let says I want to find all birds that have the tag blue & yellow & green , where blue is a must have tag and any other colours are optional.

Second level problem: Then I would like to order the query so that the birds that have all the queried colours appear first.

Is it possible to create this query in mongoDB? and if it is How could I do it?

Answer 1

You can use aggregation framework . So for the next dataset:

{ "_id":ObjectId(...), "bird":1, "tags":["blue","red","yellow","green","violet"]}
{ "_id":ObjectId(...), "bird":2, "tags":["red","yellow","green","violet"] }
{ "_id":ObjectId(...), "bird":3, "tags":["blue","yellow","violet"] }
{ "_id":ObjectId(...), "bird":4, "tags":["blue","yellow","red","violet"] }
{ "_id":ObjectId(...), "bird":5, "tags":["blue"] }

we can apply next query:

colors = ["blue","red","yellow","green"];
db.birds.aggregate(
  { $match: {tags: 'blue'} },
  { $project: {_id:0, bird:1, tags:1} },
  { $unwind: '$tags' },
  { $match: {tags: {$in: colors}} },
  { $group: {_id:'$bird', score: {$sum:1}} },
  { $sort: {score:-1} },
  { $project: {bird:'$_id', score:1, _id:0} }
)

and will get result like this:

{
  "result" : [
    { "score" : 4, "bird" : 1 },
    { "score" : 3, "bird" : 4 },
    { "score" : 2, "bird" : 3 },
    { "score" : 1, "bird" : 5 }
  ],
  "ok" : 1
}

Answer 2

Most of this you will have to do in your application. In order to find all documents where a bird has the tag "blue", you can do this:

db.collection.find( { tag: "blue" } );

Which colours are optional doesn't matter, as you have to find by the required tag anyway.

After finding them, you need to do a sort. But sorting like you want (by their 3 colours) is not something you can do in MongoDB, and something you will have to do in PHP instead.