MongoDB Aggregate multiple grouping conditions

When using aggregate for grouping, multiple grouping conditions are as follows

Native sql:

Db.test.aggregate (

{

$group: {

_id:{name: ' $name ', Pro: ' $pro},

total:{$sum: ' $num '}

}

},

{

$project: {

Total:1

}

}

)

In Java, this corresponds to the following:

Grouped according to Subjname and province dbobject groupfields = new Basicdbobject ("_id", New Basicdbobject ("Subjname", "$ Subjects.name "). Append (" Province "," $province ")); Continue adding other operation Groupfields.put such as Sum,avg ("Avgscore", New Basicdbobject ("$avg", "$subjects. Scores"));

This article is from the "Bulajunjun" blog, make sure to keep this source http://5148737.blog.51cto.com/5138737/1638112

MongoDB Aggregate multiple grouping conditions