将Mongo查询转换为Mgo查询

Question

I'm trying to retrieve all id and field2 from mongo document, if field1 equals some value and field2 exists.

Example: Mongo Document:

{

       "id": "id1"
       "field1": "val1"
       "field2": "val2"
       "field3": "val3"
}

{

      "id": "id2"
      "field1": "val4"
      "field3": "val5"
}

Result

{

    "id" : "id1"
    "field2": "val2"
}

I figured out mongodb query that works:

dbname.find( { $and: [ { "field1": "val1" }, { "field2": { $exists: true } } ] } , {"id":1, "field2":1})

But I want to call this query in Go using Mgo package. I'm unable to convert make this mongo query call using Mgo. I tried a few ways but they don't seem to be working. Can anyone help me out here?

Thank you

Answer 1

Logical AND is the default, so you can generously leave that out:

dbname.find({"field1": "val1", "field2": {$exists: true}, {"id": 1, "field2": 1})

In mgo:

In general just use a bson.M map value for each brackets (where keys must be string values). For projection use Query.Select().

sess := ... // Acquire an mgo session

c := sess.DB("dbname").C("collname") // Use your db name and collection name

var docs []bson.M
err := c.Find(bson.M{
    "field1": "val1",
    "field2": bson.M{"$exists": true},
}).Select(bson.M{"id": 1, "field2": 1}).All(&docs)

if err != nil {
    // Handle err
    log.Printf("Query error: "%v", err)
    return
}

// Process results