MongoDB search string in array of objects

You can use the $elemMatch (https://docs.mongodb.com/manual/reference/operator/projection/elemMatch/)

db.docs.find({items: {$elemMatch: {value: {$regex : "text"}}}});

So this query will find all documents with an item in the items array that contain the string "text" in the value property, after this operation you can count how much items the document has.

You can use dot notation of items.value to target the value field of all items elements, and a regular expression to perform the case-insensitive sub-string match:

db.getCollection('docs').find({ 'items.value': /text/i })

You can iterate each document and apply the indexOf, something like this..

var cursor = db.getCollection('docs').find({}); // get all docs
var newOut = []; // new array of items if match with some condition
while ( cursor.hasNext() ){ // iterate all docs

   var doc = cursor.next(); // get the document in focus
   doc.items.forEach(function(item){ // iterate the items of doc.items
       if ( item.toLowerCase().indexOf("text") !== -1 ) // check if text exists in array
           newOut.push(item); // add to new array
   });

};
printjson(newOut);