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    <p>If possible, I'd suggest that you set the condition while storing the data so that you can do a quick truth check (<code>isInStudentsList</code>). It would be super fast to do that type of query.</p> <p>Otherwise, there is a relatively complex way of using the Aggregation framework pipeline to do what you want in a single query:</p> <pre><code>db.students.aggregate( {$project: {studentId: 1, studentIdComp: "$students.id"}}, {$unwind: "$studentIdComp"}, {$project : { studentId : 1, isStudentEqual: { $eq : [ "$studentId", "$studentIdComp" ] }}}, {$match: {isStudentEqual: true}}) </code></pre> <p>Given your input example the output would be:</p> <pre><code>{ "result" : [ { "_id" : ObjectId("517b88decd483543a8bdd95b"), "studentId" : 23, "isStudentEqual" : true } ], "ok" : 1 } </code></pre> <p>A brief explanation of the steps:</p> <ol> <li>Build a projection of the document with just <code>studentId</code> and a new field with an array containing just the <code>id</code> (so the first document it would contain <code>[23, 55]</code>.</li> <li>Using that structure, <a href="http://docs.mongodb.org/manual/reference/aggregation/unwind/">$unwind</a>. That creates a new temporary document for each array element in the <code>studentIdComp</code> array.</li> <li>Now, take those documents, and create a new document projection, which continues to have the <code>studentId</code> and adds a new field called <code>isStudentEqual</code> that compares the equality of two fields, the <code>studentId</code> and <code>studentIdComp</code>. Remember that at this point there is a single temporary document that contains those two fields.</li> <li>Finally, check that the comparison value <code>isStudentEqual</code> is true and return those documents (which will contain the original document <code>_id</code> and the <code>studentId</code>. </li> <li>If the student was in the list multiple times, you might need to group the results on <code>studentId</code> or <code>_id</code> to prevent duplicates (but I don't know that you'd need that).</li> </ol>
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    1. COIts working fine, Thanks for explanation. +1
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