convertShardKeyToHashed¶

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Description描述¶

convertShardKeyToHashed(<Object>)¶: Returns the hashed value for the input. The convertShardKeyToHashed() method uses the same hashing function as the hashed index and can be used to see what the hashed value would be for a key.

Consider a sharded collection that uses a hashed shard key [1]

use test

db.orders.createIndex( { _id: "hashed" } )

sh.shardCollection( "test.orders", { _id : "hashed" } )

If the following document exists in the collection, the hashed value of the _id field is used to distribute the document:

{
  _id: ObjectId("5b2be413c06d924ab26ff9ca"),
  "item" : "Chocolates",
  "qty" : 25
}

To determine the hashed value of _id field used to distribute the document across the shards, you can use the convertShardKeyToHashed method:

convertShardKeyToHashed( ObjectId("5b2be413c06d924ab26ff9ca") )

[1]	If the collection already contains data, you must create a hashed index on the shard key before you shard the collection. For an empty collection, MongoDB creates the index as part of `sh.shardCollection()`.