Search on long data type field in MongoDB and Java

Aditi_Barde · October 6, 2021, 4:06pm

Hi All,
I’m taking a number input from user. I have to fetch documents having priceId (which has data field of type long) starting with the input taken from user.
for example, if user inputs 9, I need to fetch 9,99,900,9180 etc.

I tried to use {$where: ‘/^9/.test(this.priceId)’} but this fetches no results.

I have the below which works but I’m not able to find its java equivalent code.
{
“$expr”: {
“$regexMatch”: {
“input”: {"$toString": “$priceId”},
“regex”: /^9/
}
}
}

Can someone please help me with this?

MaBeuLux88 · October 6, 2021, 10:28pm

Hi @Aditi_Barde and welcome in the MongoDB Community !

First, I created a little collection test.coll in my localhost MongoDB:

> db.coll.find()
[
  { _id: ObjectId("615e1078ad5e77708f9a2381"), nb: Long("912") },
  { _id: ObjectId("615e10c3ad5e77708f9a2382"), nb: Long("123") },
  { _id: ObjectId("615e10cdad5e77708f9a2383"), nb: Long("909") }
]

I used your existing aggregation in MongoDB Compass to test it. Looks like it is working just fine.
Using the export pipeline code to language button, I export the code into the Java language:

Now I copy paste this into a little Java class using the MongoDB Driver Sync 4.3.3.

I end up with something like this:

import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;
import org.bson.json.JsonWriterSettings;

import java.util.List;
import java.util.function.Consumer;
import java.util.regex.Pattern;

import static java.util.Collections.singletonList;

public class Community {

    public static void main(String[] args) {
        String connectionString = "mongodb://localhost";
        try (MongoClient mongoClient = MongoClients.create(connectionString)) {
            MongoDatabase db = mongoClient.getDatabase("test");
            MongoCollection<Document> coll = db.getCollection("coll");
            List<Document> pipeline = singletonList(new Document("$match", new Document("$expr", new Document("$regexMatch",
                                                                                                              new Document(
                                                                                                                      "input",
                                                                                                                      new Document(
                                                                                                                              "$toString",
                                                                                                                              "$nb")).append(
                                                                                                                      "regex",
                                                                                                                      Pattern.compile(
                                                                                                                              "^9"))))));
            coll.aggregate(pipeline).forEach(printDocuments());
        }
    }

    private static Consumer<Document> printDocuments() {
        return doc -> System.out.println(doc.toJson(JsonWriterSettings.builder().indent(true).build()));
    }
}

Once executed, it returns only the 2 documents starting with a “9”.

{
  "_id": {
    "$oid": "615e1078ad5e77708f9a2381"
  },
  "nb": 912
}
{
  "_id": {
    "$oid": "615e10cdad5e77708f9a2383"
  },
  "nb": 909
}

I can now improve the generated Java code and use the driver helpers a bit more to make the code easier to read.

Actually, before I do that, I can simplify the pipeline a little bit so it’s easier to read & write:

[
  {
    '$addFields': {
      'nb': {
        '$toString': '$nb'
      }
    }
  }, {
    '$match': {
      'nb': /^9/
    }
  }
]

In Java now it looks like this when I use the Aggregates helpers + static imports:

package com.mongodb.quickstart;

import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.model.Field;
import org.bson.Document;
import org.bson.conversions.Bson;
import org.bson.json.JsonWriterSettings;

import java.util.List;
import java.util.function.Consumer;

import static com.mongodb.client.model.Aggregates.*;
import static com.mongodb.client.model.Filters.regex;
import static java.util.Arrays.asList;

public class Community {

    public static void main(String[] args) {
        String connectionString = "mongodb://localhost";
        try (MongoClient mongoClient = MongoClients.create(connectionString)) {
            MongoDatabase db = mongoClient.getDatabase("test");
            MongoCollection<Document> coll = db.getCollection("coll");
            Bson set = set(new Field<>("nb", new Document("$toString", "$nb")));
            Bson match = match(regex("nb", "^9"));
            List<Bson> pipeline = asList(set, match);
            coll.aggregate(pipeline).forEach(printDocuments());
        }
    }

    private static Consumer<Document> printDocuments() {
        return doc -> System.out.println(doc.toJson(JsonWriterSettings.builder().indent(true).build()));
    }
}

As you can see, it’s much better & easier to read ! I think this is the easiest way to write this pipeline using the MongoDB Java driver. I don’t know if your version or mine are equivalent in performances, but I don’t expect a big difference between the 2 to be honest.
I don’t think there is an helper in the Java Driver to write the $expr combined with the $regexMatch. There is Filters.expr that you can use but the regexMatch will have to be written with Document & BsonDocuments I guess.

Cheers,
Maxime.