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POPlay! framework morphia module group aggregation by date bucket
 

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  1. POPlay! framework morphia module group aggregation by date bucket
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    <p>I'm using the Play! framework morphia-mongodb module, and I see it has nice built-ins for doing group aggregation. Unfortunately all the examples only show grouping/aggregating by a fixed field, whereas I need to aggregate by a calculated field: timestamp grouped by day. I'm wondering if anyone knows the right approach to this?</p> <p>I know I can just resort to a native map/reduce (which itself took a little digging to figure out, so I'm posting here for reference, using Movies and showtimes):</p> <pre><code> DBCollection coll = Movie.col(); String map = "function() { " + (this.showtime.getMonth() + 1) + '/' + this.showtime.getDate()}; " + "var key = {date: this.showtime.getFullYear() + '/' + (this.showtime.getMonth() + 1) + '/' + this.showtime.getDate()}; " + "emit(key, {count: 1}); }"; String reduce = "function(key, values) { var sum = 0; " + " values.forEach( function(value) {sum += value['count'];} );" + " return {count: sum}; }"; String output = "dailyShowingCount"; MapReduceOutput out = coll.mapReduce( map, reduce, output, MapReduceCommand.OutputType.REPLACE, null); SimpleDateFormat df = new SimpleDateFormat("yyyy/MM/dd"); for (Iterator&lt;DBObject&gt; itr = out.results().iterator(); itr.hasNext();) { DBObject dbo = itr.next(); String compoundKeyStr = dbo.get("_id").toString(); String compoundValStr = dbo.get("value").toString(); DBObject compKey = (DBObject)JSON.parse(compoundKeyStr); DBObject compVal = (DBObject)JSON.parse(compoundValStr); //don't know why count returns as a float, but it does, so i need to convert Long dCount = new Double( Double.parseDouble(compVal.get("count").toString()) ).longValue(); Date date = df.parse(compKey.get("date").toString()); } </code></pre> <p>But if there's already an elegant built-in way to do this aggregation with the morphia module, I'd like to use that instead. One thought I had was to create a virtual field in my java class (e.g. "getDay()") and then group/aggregate by that. Does anyone have experience with this?</p>
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