db.testcase.drop();
db.testcase.insert( { a : [

{ x : 1 }

,

{ x : 2 }

,

{ x : 3 }

,

{ x : 4 }

] } )

function test(){
print( db.testcase.find(
{
a :

{ x : 1 }

,
"$or" : [ { a :

{ x : 2 }

} , { a :

{ x : 3 }

} ]
}
).count() )
}

// The first find will return a result since there isn't an index
test();

// Now create an index

db.testcase.ensureIndex(

{"a":1}

)

// The same query will not return data now
test();

// Drop the indexes

db.testcase.dropIndexes()

// And it will return data again
test()