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POHow do I keep documents in aggregation with $unwind
 

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  1. POHow do I keep documents in aggregation with $unwind
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    <p>Lets say I have three students...</p> <p>Alice, she is Always there on fridays.</p> <pre><code>{ "name" : "Alice", "goes" : { "mondays" : { "fr" : 900, "to" : 1400 }, "fridays" : { "fr" : 700, "to" : 1600 }, } } </code></pre> <p>And bob, here should be there on the first of january</p> <pre><code>{ "_id" : ObjectId("5284a7085d60338b40b8f17d"), "name" : "Bob", "goes" : { "mondays" : { "fr" : 800, "to" : 1200 }, "special" : [ { "date" : "2010-01-01", "fr" : 1000, "to" : 1500 } ] } } </code></pre> <p>And Clair who will not be attenging on mondays or at 10.00 </p> <pre><code>{ "_id" : ObjectId("5284c2785d60338b40b8f17f"), "name" : "Clair", "goes" : { "wednesdays" : { "fr" : 1100, "to" : 1500 }, "special" : [ { "date" : "2010-01-01", "fr" : 1600, "to" : 1900 }, { "date" : "2010-01-02", "fr" : 1000, "to" : 1300 } ] } } </code></pre> <p>I want to find all students that should attend on fridays at 7 och 10 on the first of January 2010</p> <p>So I do this with the aggregation framework.</p> <pre><code>db.students.aggregate( [ { $unwind: "$goes.special" }, { $match: { $or : [ { 'goes.fridays.fr': 700, }, { 'goes.special.date' : '2010-01-01', 'goes.special.fr': 1000 } ] } } ] ) </code></pre> <p>But Alice does not show up. It clearly states why in the mongodb docs, <a href="http://docs.mongodb.org/manual/reference/operator/aggregation/unwind/" rel="nofollow">http://docs.mongodb.org/manual/reference/operator/aggregation/unwind/</a> at the very bottom.</p> <blockquote> <p>"If you specify a target field for $unwind that holds an empty array ([]) in an input document, the pipeline ignores the input document, and will generates no result documents."</p> </blockquote> <p>I could solve it by adding an array with a null value in it but that does not seam like a nice solution.</p> <p>Is there a way I could get unwind NOT to ignore documents that does not have data in a $unwind'ed array?</p>
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    1. USJoelbitar
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    1. COIs there any need for `$unwind`ed result, other than what you mentioned in your question?
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      1. USAmol M Kulkarni
 

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