Case insensitive sorting in MongoDB

问题

How can I sort a MongoDB collection by a given field, case-insensitively? By default, I get A-Z before a-z.

I'm using Java.

回答1:

Update: As of now mongodb have case insensitive indexes:

Users.find({})
  .collation({locale: "en" })
  .sort({name: 1})
  .exec()
  .then(...)

shell:

db.getCollection('users')
  .find({})
  .collation({'locale':'en'})
  .sort({'firstName':1})

---

Update: This answer is out of date, 3.4 will have case insensitive indexes. Look to the JIRA for more information https://jira.mongodb.org/browse/SERVER-90

---

Unfortunately MongoDB does not yet have case insensitive indexes: https://jira.mongodb.org/browse/SERVER-90 and the task has been pushed back.

This means the only way to sort case insensitive currently is to actually create a specific "lower cased" field, copying the value (lower cased of course) of the sort field in question and sorting on that instead.

回答2:

Sorting does work like that in MongoDB but you can do this on the fly with aggregate:

Take the following data:

{ "field" : "BBB" }
{ "field" : "aaa" }
{ "field" : "AAA" }

So with the following statement:

db.collection.aggregate([
    { "$project": {
       "field": 1,
       "insensitive": { "$toLower": "$field" }
    }},
    { "$sort": { "insensitive": 1 } }
])

Would produce results like:

{
    "field" : "aaa",
    "insensitive" : "aaa"
},
{
    "field" : "AAA",
    "insensitive" : "aaa"
},
{
    "field" : "BBB",
    "insensitive" : "bbb"
}

The actual order of insertion would be maintained for any values resulting in the same key when converted.

回答3:

This has been an issue for quite a long time on MongoDB JIRA, but it is solved now. Take a look at this release notes for detailed documentation. You should use collation.

User.find()
    .collation({locale: "en" }) //or whatever collation you want
    .sort({name:1})
    .exec(function(err, users) {
        // use your case insensitive sorted results
    });

回答4:

As of now (mongodb 4), you can do the following:

mongo shell:

db.getCollection('users')
  .find({})
  .collation({'locale':'en'})
  .sort({'firstName':1});

mongoose:

Users.find({})
  .collation({locale: "en" })
  .sort({name: 1})
  .exec()
  .then(...)

Here are supported languages and locales by mongodb.

回答5:

Here it is in Java. I mixed no-args and first key-val variants of BasicDBObject just for variety

        DBCollection coll = db.getCollection("foo");

        List<DBObject> pipe = new ArrayList<DBObject>();

        DBObject prjflds = new BasicDBObject();
        prjflds.put("field", 1);
        prjflds.put("insensitive", new BasicDBObject("$toLower", "$field"));

        DBObject project = new BasicDBObject();
        project.put("$project", prjflds);
        pipe.add(project);

        DBObject sort = new BasicDBObject();
        sort.put("$sort", new BasicDBObject("insensitive", 1));
        pipe.add(sort);

        AggregationOutput agg = coll.aggregate(pipe);

        for (DBObject result : agg.results()) {
            System.out.println(result);
        }

回答6:

Adding the code .collation({'locale':'en'}) helped to solve my issue.

回答7:

We solve this problem with the help of .sort function in JavaScript array

Here is the code

    function foo() {
      let results = collections.find({
        _id: _id
      }, {
        fields: {
          'username': 1,
        }
      }).fetch();

      results.sort((a, b)=>{
        var nameA = a.username.toUpperCase();
        var nameB = b.username.toUpperCase();

        if (nameA  nameB) {
          return 1;
        }
        return 0;
      });

      return results;
    }

来源：https://stackoverflow.com/questions/22931177/case-insensitive-sorting-in-mongodb