8

I am using Spring Boot and Spring Data MongoDB to interface with an underlying sharded MongoDB cluster. My Spring Boot Application access the cluster via a mongos router.

Using Spring Data MongoDB, you can specify the collection an object is persisted to via @Document(collection = "nameOfCollection"), or it defaults to the class name (first letter lowercase). These collections do not need to exist before-hand; they can be created at runtime.

To shard a collection in MongoDB, you need to

1 - Enable sharding on the Database: sh.enableSharding("myDb")

2 - Shard the collection on a sharded database: sh.shardCollection("myDb.myCollection", {id:"hashed"})

Assuming there is an existing sharded database, does Spring Data MongoDB offer a way to shard a collection with a shard key? As far as I can tell, I cannot shard a collection with Spring, and therefore must configure the sharded collection before my Boot application runs. I find it odd that Spring would allow me to use undefined collections, but does not provide a way to configure the collection.

Edit: I have seen both Sharding with spring mongo and How configuring access to a sharded collection in spring-data for mongo? which refer more to the deployment of a sharded MongoDB cluster. This question assumes all the plumbing is there and that the collection itself simply must be sharded.

Chris
  • 387
  • 5
  • 16

3 Answers3

4

Despite this question being old, I've got the same question, and it looks like there is away to provide custom sharding key since recently.

Annotation-based Shard Key configuration is available on spring-data-mongodb:3.x, https://docs.spring.io/spring-data/mongodb/docs/3.0.x/reference/html/#sharding

@Document("users")
@Sharded(shardKey = { "country", "userId" }) 
public class User {

    @Id
    Long id;

    @Field("userid")
    String userId;

    String country;
}

As of today spring-boot-starter-mongodb comes with 2.x version though.

Paulius
  • 444
  • 5
  • 12
  • This is available in spring-data-mongodb 3.0 as per the documentation https://docs.spring.io/spring-data/mongodb/docs/current-SNAPSHOT/reference/html/#new-features.3.0. However, i could not find the maven dependency. Is spring-data-mongodb 3.0 available for use? – java_geek Apr 02 '20 at 13:42
  • You can use it with spring-boot version 2.3.0.M3 which can be pulled from snapshot repositories. Installation guide: https://docs.spring.io/spring-boot/docs/2.0.0.M3/reference/htmlsingle/#getting-started-installing-spring-boot – Paulius Apr 03 '20 at 09:30
2

Was running into the same problem with our update queries that internally used a save().

How it was solved?

So I now have overridden the spring-data-mongo core dependency from spring-boot-starter which is 2.1.x by 3.x release in our model which is now supporting @Sharded() annotation .

<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-mongodb</artifactId>
<version>3.1.5</version>
</dependency>

allows you to say

@Document(collection = "hotelsdevice")
@Sharded(shardKey = { "device" })

public class Hotel extends BaseModel {

which internally is now able to tell the underlying mongo which is our shardkey. I am assuming this will further fix our count() queries too which were failing due to the same error "query need to target a shard "

sainik dasgupta
  • 21
  • 1
  • This is the solution, notice if Document or Sharded annotation values do not match your Azure resource, CosmosDB will fail with confusing error "query in command must target a single shard key" – BabyishTank Sep 01 '23 at 21:41
1

Even though this is not a Spring Data solution, a potential workaround is posed in how to execute mongo admin command from java, where DB can be acquired from a Spring MongoTemplate.

DB db = mongo.getDB("admin");
DBObject cmd = new BasicDBObject();
cmd.put("shardcollection", "testDB.x");
cmd.put("key", new BasicDBObject("userId", 1));
CommandResult result = db.command(cmd);
Chris
  • 387
  • 5
  • 16