> db.test1.drop()
true
> db.test1.createIndex({ a: 1, b: 1 }, { unique: true, partialFilterExpression: { c: { $eq: 'MyClass1' } } })
{
        "createdCollectionAutomatically" : true,
        "numIndexesBefore" : 1,
        "numIndexesAfter" : 2,
        "ok" : 1
}
> db.test1.insert({a: 1, b: 1, c: 'MyClass1'})
WriteResult({ "nInserted" : 1 })
> db.test1.insert({a: 1, b: 2, c: 'MyClass1'})
WriteResult({ "nInserted" : 1 })
> db.test1.insert({a: 2, b: 1, c: 'MyClass1'})
WriteResult({ "nInserted" : 1 })
> db.test1.insert({a: 2, b: 2, c: 'MyClass1'})
WriteResult({ "nInserted" : 1 })
> db.test1.insert({a: 2, b: 2, c: 'MyClass2'})
WriteResult({ "nInserted" : 1 })
> db.test1.insert({a: 2, b: 2, c: 'MyClass1'})
WriteResult({
        "nInserted" : 0,
        "writeError" : {
                "code" : 11000,
                "errmsg" : "E11000 duplicate key error collection: project1.test1 index: a_1_b_1 dup key: { : 2.0, : 2.0 }"
        }
})
> db.test1.find()
{ "_id" : ObjectId("56d785be814898458ee50253"), "a" : 1, "b" : 1, "c" : "MyClass1" }
{ "_id" : ObjectId("56d785c1814898458ee50254"), "a" : 1, "b" : 2, "c" : "MyClass1" }
{ "_id" : ObjectId("56d785c6814898458ee50255"), "a" : 2, "b" : 1, "c" : "MyClass1" }
{ "_id" : ObjectId("56d785c9814898458ee50256"), "a" : 2, "b" : 2, "c" : "MyClass1" }
{ "_id" : ObjectId("56d785cd814898458ee50257"), "a" : 2, "b" : 2, "c" : "MyClass2" }
> db.test1.createIndex({ a: 1, b: 1 }, { unique: true, partialFilterExpression: { c: { $eq: 'MyClass3' } } })
{
        "ok" : 0,
        "errmsg" : "Index with name: a_1_b_1 already exists with different options",
        "code" : 85
}
>