performing priority query in mongo - regex

Question

sample document :
{"name":"John", "age":35, "address":".....",.....}
Employees whose join_month=3 is priority 1
Employees whose address contains the string "Avenue" is priority 2
Employees whose address contains the string "Street" is priority 3
Employees whose address contains the string "Road" is priority 4
As of now, I'm at this stage:
db.collection.aggregate([
{ "$match": {
"$or": [
{ "join_month": 3 },
{ "address": /.*Avenue.*/i },
{ "address": /.*Street.*/i },
{ "address": /.*Road.*/i }
]
}},
{ "$project": {
"name": 1,
"age": 1,
"_id": 0,
"priority": { ?????????? }
}},
{ "$sort": { "priority": 1 } }
])
I'm stuck at priority field. What should I put there?

Answer 1

Using the aggregation framework you would "ideally" want to use the $regex filter within the $cond logical operator in the $project pipeline step but unfortunately MongoDB is yet to support this.
There is a JIRA ticket for this currently open $project filter using $regex
However, a workaround (though not the best solution performant-wise) would be to use map-reduce. Consider populating a test collection:
db.test.insert([
{ _id: 0, "join_month": 12, "address": "33 Point Avenue", "name": "John", "age":35 },
{ _id: 1, "join_month": 10, "address": "2A Broad Street, Surbub", "name": "Jane", "age":21 },
{ _id: 2, "join_month": 3, "address": "127 Umpstreeten Road, Surbub", "name": "Alan", "age":63 },
{ _id: 3, "join_month": 3, "address": "127 Umpstreeten Road, Surbub", "name": "Louise", "age":30 }
])
Define your map function as:
var mapper = function() {
var priority;
if (this.join_month==3){
priority = 1;
}
else if (this.address.match(/Avenue/i)){
priority = 2;
}
else if (this.address.match(/Street/i)){
priority = 3;
}
else if (this.address.match(/Road/i)){
priority = 4;
}
else {
priority = 99;
}
var value = {
"name": this.name,
"age": this.age,
"priority": priority
};
emit( this._id, value );
};
The reduce function follows:
var reducer = function() { };
Then run the mapduce operation on the test collection and store the result in the collection mr_result
db.test.mapReduce(mapper, reducer, {
"out": 'mr_result'
"query": {
"$or": [
{ "join_month": 3 },
{ "address": /.*Avenue.*/i },
{ "address": /.*Street.*/i },
{ "address": /.*Road.*/i }
]
}
})
Query the result collection:
db.mr_result.find().sort({ "priority": 1})
Sample Output
{ "_id" : 2, "value" : { "name" : "Alan", "age" : 63, "priority" : 1 } }
{ "_id" : 3, "value" : { "name" : "Louise", "age" : 30, "priority" : 1 } }
{ "_id" : 0, "value" : { "name" : "John", "age" : 35, "priority" : 2 } }
{ "_id" : 1, "value" : { "name" : "Jane", "age" : 21, "priority" : 3 } }