使用PHP基于Condition更新MongoDB子文档元素

Question

Here is my JSON Array

{
"_id" : ObjectId("563b57c84abf457b395076f0"),
"project_id" : "563b57c84abf45ce1f5076f1",
"project_task" : [ 
    {
        "switch" : "Ball",
        "deviceId" : "dasdqwdf124",
        "slot" : "2344",
        "MigrationStartDate" : "",
        "MigrationEndDate" : "",
        "MigrationStatus" : "",
        "task_id" :12
    }
  ]
}

In this array project_id and task_id (Sub Document element) values are unique.
So in this case i need update my sub document element one at a time
When project_id and task_id are equals to given values. So far i used update function with and condition and findAndModify() function but never worked for me.
Here is my Query using findAndModify()

findAndModify(array('project_id' => "$projectId", 'project_task' => array('task_id' => "$taskId")), array('$set' => array("$column" => "$value")))  

Please help me out