MongoDB using MapReduce to filter fields by text content

Let's say that we want to filter a list of documents and extract only those in which the text of one of the fields matches a given constraint, for example a word that is repeated in the text

For this example I will be doing it using MongoDB's MapReduce

Simple JSON Model

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{       "_id" : "507f191e810c19729de860ea",       "txtField" : "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus mauris arcu, lacinia a pharetra id, rhoncus in lorem. Morbi tempor consequat ante, vel porta tellus lacinia id. Phasellus vel nisi vitae velit pulvinar tincidunt non id massa. " }

Below is the Map/Reduce functions that I will be applying to filter my results the results :

1.- Map Function

Map function

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function Map() {         // count the number of times the regexp is matched in the text for the field txtField      var count = this.txtField.match(/lorem/gi);       // emit the result when the pattern has been matched at least 2 times     if( count != null && count.length > 1){        emit(this._id,count);    }       }

2.- Reduce Function

Reduce function

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function Reduce(key, values) {    return values[0]; }

3.- Full query

full query

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db.runCommand({      mapreduce: "MY_DOCS",      map : function Map() {           var count = this.txtField.match(/lorem/gi);                if( count != null && count.length > 1){            emit(this._id,count);          }                  },     reduce : function Reduce(key, values) {        return values[0];     },     query : { "txtField" : { "$exists" : true } },     out : { inline : 1 } });

You can find additional info on MapReduce operations this nice article