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POPerforming case-statement in mongodb aggregation framework
 

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  1. POPerforming case-statement in mongodb aggregation framework
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    <p>I'm evaluating how well the MongoDB aggregation framework suits our needs as we are currently running on top of SQL Server. I'm having a hard time performing a specific query:</p> <p>Say I have the following pseudo records (modeled as columns in a sql table and as a full document in a mongodb collection)</p> <pre><code>{ name: 'A', timespent: 100, }, { name: 'B', timespent: 200, }, { name: 'C', timespent: 300, }, { name: 'D', timespent: 400, }, { name: 'E', timespent: 500, } </code></pre> <p>I want to group the timespent field in to ranges and count the occurrences so I will get e.g. the following pseudo-records:</p> <pre><code>results{ 0-250: 2, 250-450: 2, 450-650: 1 } </code></pre> <p>Note that these ranges (250, 450 and 650) are dynamic and will likely be altered over time by the user. In SQL we extracted the results with something like this:</p> <pre><code>select range, COUNT(*) as total from ( select case when Timespent &lt;= 250 then '0-250' when Timespent &lt;= 450 then '200-450' else '450-600' end as range from TestTable) as r group by r.range </code></pre> <p>Again, note that this sql is constructed dynamically by our app to fit the specific ranges available at any one time. </p> <p>I'm struggling to find the appropriate constructs in the mongodb aggregation framework to perform such queries. I can query for the results of a single range by inserting a $match into the pipeline(i.e. getting the result of a single range) but I cannot grok how to extract all the ranges and their counts in a single pipeline query. </p>
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