MongoDB Length of String or need help in mongoDB mapReduce query - mongodb

Question

I need some guidence in a query for mongodb. I have a collection of items which contain an array that contains multiple fields, but I only care about one field, which is the barcode field. I need to distiguish the length of the barcode string.
Items.find({this.array['barcode'].length > 6})
It would be great if the above query was possible, but I believe that it's not. I only need a list of barcodes. How do I go about solving this problem? Does mongodb have something to compare length of a string? Or do I have to use a mapReduce query? If I do could I have some guidence on that? I'm not sure how I would go about writing it.
Thank you

Answer 1

Try using a regular expression.
/^\w{6}/ this says match a word that has 6 word characters at the start of the string.
Example:
Setup:
user test;
var createProduct = function(name, barcode){
return {
name : name,
detail: {
barcode : barcode
}
};
};
db.products.drop();
for(var i = 0; i < 10; i++){
db.products.insert( createProduct( "product" + i, "1234567890".substring(0,i+1) ));
}
Document structure:
{
"_id" : ObjectId("540d3ba1242ff352caa6154b"),
"name" : "product0",
"detail" : {
"barcode" : "1"
}
}
Query:
db.products.find({ "detail.barcode" : /^\w{6}/ })
Output:
{ "_id" : ObjectId("540d3ba1242ff352caa61550"), "name" : "product5", "detail" : { "barcode" : "123456" } }
{ "_id" : ObjectId("540d3ba1242ff352caa61551"), "name" : "product6", "detail" : { "barcode" : "1234567" } }
{ "_id" : ObjectId("540d3ba1242ff352caa61552"), "name" : "product7", "detail" : { "barcode" : "12345678" } }
{ "_id" : ObjectId("540d3ba1242ff352caa61553"), "name" : "product8", "detail" : { "barcode" : "123456789" } }
{ "_id" : ObjectId("540d3ba1242ff352caa61554"), "name" : "product9", "detail" : { "barcode" : "1234567890" } }
However, if barcode is a key within an object inside an array AND you only want the matched barcode values. Then you should use an aggregate function to extract the values.
Setup:
user test;
var createProduct = function(name){
var o = {
name : name,
subProducts: []
};
for(var i = 0; i < 10; i++){
o.subProducts.push({
barcode : "1234567890".substring(0,i+1)
});
}
return o;
};
db.products.drop();
db.products.insert( createProduct( "newBrand") );
Document Structure:
{
"_id" : ObjectId("540d4125242ff352caa61555"),
"name" : "newBrand",
"subProducts" : [
{
"barcode" : "1"
},
...
{
"barcode" : "123456789"
},
{
"barcode" : "1234567890"
}
]
}
Aggregate Query:
db.products.aggregate([
{ $unwind : "$subProducts" },
{ $match : { "subProducts.barcode" : /^\w{6}/ } }
]);
Output:
{ "_id" : ObjectId("540d4125242ff352caa61555"), "name" : "newBrand", "subProducts" : { "barcode" : "123456" } }
{ "_id" : ObjectId("540d4125242ff352caa61555"), "name" : "newBrand", "subProducts" : { "barcode" : "1234567" } }
{ "_id" : ObjectId("540d4125242ff352caa61555"), "name" : "newBrand", "subProducts" : { "barcode" : "12345678" } }
{ "_id" : ObjectId("540d4125242ff352caa61555"), "name" : "newBrand", "subProducts" : { "barcode" : "123456789" } }
{ "_id" : ObjectId("540d4125242ff352caa61555"), "name" : "newBrand", "subProducts" : { "barcode" : "1234567890" } }
More info:
http://docs.mongodb.org/manual/reference/operator/query/regex/
Retrieve only the queried element in an object array in MongoDB collection