CODEWITHSUNDEEP
amazon-web-servicesamazon-dynamodb
sandeep kumar
sandeep kumar

Reputation: 11

DynamoDB conditional put

Say I want to add a record like below:

{
id:876876,
username:example,
email:[email protected],
phone:xxxxxxx,
created_at:current_date,
updated_at:current_date
}

What I want is to check with the id if record exist created_date should not be modified only updated_date should have current_date.

Can we do this with put method without having to be making a get item call?

Upvotes: 1

Views: 387

Answers (1)

Ashok JayaPrakash
Ashok JayaPrakash

Reputation: 2283

To create a new item or update an existing item with conditional expression. Prefer to use updateItem rather than putItem.

If the Hash key (Primary key) doesn't exist both putItem and updateItem create a new record. If the record already exist, putItem will completely override the existing row but updateItem only updates the attributes passed in UpdateExpression not a whole record.

In your case, use if_not_exists() function to check whether the created_at field already exists or not. If exists created_at will not be overridden.

Update expression: "SET #email = :email, #created_at = if_not_exists(#created_at, :created_at), #updated_at = :updated_at"

Sample snippet

var params = {
    ExpressionAttributeNames: {
     "#email": "email", 
     "#created_at": "created_at",
     "#updated_at": "updated_at"
    }, 
    ExpressionAttributeValues: {
     ":email": {
       S: "[email protected]"
      }, 
     ":created_at": {
       S: date.toISOString()
      },
      ":updated_at": {
        S: date.toISOString()
    }
    }, 
    Key: {
     "id": {
       S: "T1"
      }
    }, 
    ReturnValues: "ALL_NEW", 
    TableName: "stack", 
    UpdateExpression: "SET #email = :email, #created_at = if_not_exists(#created_at, :created_at), #updated_at = :updated_at"
   };
   ddb.updateItem(params, function(err, data) {
     if (err) console.log(err, err.stack); // an error occurred
     else     console.log(data);  
   })

Upvotes: 1

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