{
"_id" : ObjectId (" 5994 f94bd451d806e88f13d3 "),
"Task_id" : [
The ObjectId (" 5994 fa8609a1d40006b11b07 ")
]
}

In the view of how the elements of the array into a operation, remove the two [], in the way is in view of the database operation, not use the code to change