MongoDB showing error when it finds a blank entry - php

Question

I have a project where it searches for a specific entry in a specific column and then returns all documents that have that entry in that column. It works almost perfectly except when that entry field is empty it gives an error. Let me try to illustrate below.
My DB:
A|B|C|D
1|1|5|5
2|1| |6
3|2|7|7
4|2|8|8
My PHP:
$query = array( "B" => 1);
$cursor = $collection->find( $query );
foreach ($cursor as $obj) {
echo $obj["A"] . $obj["B"] . $obj["C"] .$obj["D"] . "<br />";
}
My output is:
1155
21Notice: Undefined index: C6
How do I go about not giving any errors. Just treat it as an empty field. I'm not sure if this is a common problem but, I'm still new to PHP and very new to MongoDB.

Answer 1

Use isset() to find out if the key exists in the array before trying to index using it
foreach ($cursor as $obj) {
echo $obj["A"] . $obj["B"]. (isset($obj["C"]) ? $obj["C"] : '' ) .$obj["D"]."<br />";
//It will replace each blank with an ''
}

Answer 2

I believe thats nothing to do with mongodb. Its how the flexible document schema works. It wont return the field because the key C doesnt exist in the particular document.
I dont have any experience with PHP. But am sure php throws the error because you are trying to access the key 'C' that doesnt exist in the particular document.
But i believe these problems can easily be solved if you use some ODM (Object document mappers). It solves the problem by assigning default value based on the data type of the field.
Hope it helps