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POProjecting a sub query in mongo
 

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  1. POProjecting a sub query in mongo
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    <p>I am using a dynamic form builder to store values into mongo. Meaning the fields are defined at runtime.</p> <p>Now I am trying to let the user build a dynamic grid view of data so that they can choose which fields they want to see at a glance. Thus I need to project a subset of fields stored in a collection item.</p> <p>Here is an example of 2 records in the collection</p> <pre><code>{ "_id": { "$oid": "511ff0a8521e66d41b0d35d6" }, "FormID": { "$uuid": "413ba627-94bf-0ca7-49b3-9ca2a1a3e9b5" }, "ResultID": { "$uuid": "45f455ae-8486-aaa9-b97a-e480bfdf3db4" }, "FieldValues": [ { "FieldID": "first name", "FieldValue": "John" }, { "FieldID": "last name", "FieldValue": "smith" }, { "FieldID": "school", "FieldValue": "high school" }, { "FieldID": "favorite subject", "FieldValue": "math" }, ] }, { "_id": { "$oid": "511ff0a8521e66d41b0d35d7" }, "FormID": { "$uuid": "413ba627-94bf-0ca7-49b3-9ca2a1a3e9b5" }, "ResultID": { "$uuid": "45f455ae-8486-aaa9-b97a-e480bfdf3db5" }, "FieldValues": [ { "FieldID": "first name", "FieldValue": "sarah" }, { "FieldID": "last name", "FieldValue": "smith" }, { "FieldID": "school", "FieldValue": "high school" }, { "FieldID": "favorite subject", "FieldValue": "english" }, ] }, </code></pre> <p>Let's say I wanted to project Result Id, First Name, Last Name</p> <p>In SQL -- I would have had FieldValues defined in its own table, and I would have done a sub query on Field values where ResultId = (parent's result id) and FieldID = "first name", then another sub query on "last name" and so on to flatten out the results.</p> <p>I've been trying to figure out how to do this with mongo. I was able to find the $slice operator, but that only lets you get a consecutive set of array elements.</p> <p>The reason why I don't want to get the whole document is that in some cases my customers have defined 400+ fields to track. Deserializing all of that on even 200 rows can mean 100MB of data passed over the network and deserialized (slow).</p> <p>Any advice / suggestions would be appreciated</p>
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    1. USapexdodge
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    1. COcurious why you tagged the question with mapreduce?
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      1. USAsya Kamsky
    2. COI think there is a way to do this in mapreduce so people who follow that tag might be able to help. But I knew that aggregation framework was also a possibility
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