can't update item in DynamoDB

Question

I have been trying to figure out how to update an item in dynamoDB but have not had any success.

I know how to add and item and remove an item but not update.

Here Is my code:

dynamoDB.updateItem({
    "TableName": "mytable",
    "Key": {
        "thing_ID": {"S": "0000"}
    },
    "UpdateExpression": "SET",
    "ExpressionAttributeNames": {
        "SessionID": ""
    },
    "ExpressionAttributeValues": {
        "SessionID": {
            "S": "maybe this works",
        }
    }
})

Answer 1

It looks like you are trying to update an item by using an Expression, and in this case, your UpdateExpression is incorrect. Both the ExpressionAttributeNames and ExpressionAttributeValues are used for placeholder substitution in your expression.

I think your code would look something like this, if you want to set an attribute for an item:

dynamoDB.updateItem({  
    "TableName" : "exampleTable",
    "Key" : {
        "hashAttributeName" : {
            "S" : "thing_ID"
        }
    },
    "UpdateExpression" : "SET #attrName =:attrValue",
    "ExpressionAttributeNames" : {
        "#attrName" : "SessionID"
    },
    "ExpressionAttributeValues" : {
        ":attrValue" : {
            "S" : "maybe this works"
        }
    }
});

This will update an item that looks like this:

{  
    "Item":{  
        "hashAttributeName":"thing_ID"
    }
}

To this:

{  
    "Item":{  
        "hashAttributeName" : "thing_ID",
        "SessionID" : "maybe this works"
    }
}

Answer 2

Here's an example using AWS SDK for JavaScript v2.1.33.

The complete example is here: https://github.com/mayosmith/HelloDynamoDB/blob/master/HelloDynamoDB.html

/*
-----------------------------------------------------------------
AWS configure
Note: this is a simple experiement for demonstration
purposes only. Replace the keys below with your own.
Do not include the secret key in an actual production
environment, because, then, it wont be secret anymore...
-----------------------------------------------------------------
*/
AWS.config.update({accessKeyId: 'AKIAJUPWRIYYQGDB6AFA', secretAccessKey: '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'});
// Configure the region
AWS.config.region = 'us-west-2';  //us-west-2 is Oregon
//create the ddb object
var ddb = new AWS.DynamoDB();
/*
-----------------------------------------------------------------
Update the Table
-----------------------------------------------------------------
*/
//update the table with this data
var params = {
  Key: {
    name: {S: 'John Mayo-Smith'},
    city: {S: 'New York'}
  },
  AttributeUpdates: {
    food: {
      Action: 'PUT',
      Value: {S: 'chocolate'}
    }
  },
  TableName: 'sampletable',
  ReturnValues: 'ALL_NEW'
};
//update the table
update();
/*
-----------------------------------------------------------------
Get Item from the Table
-----------------------------------------------------------------
*/
//attribute to read
var readparams = {

  Key: {
    name: {S: 'John Mayo-Smith'},
    city: {S: 'New York'}
  },
  AttributesToGet: ['food'],
  TableName: 'sampletable'
};
//get the item
read();
/*
-----------------------------------------------------------------
function update()
Description: Calls updateItem which is part of the AWS Javascript
SDK.
Returns: JSON object (the object is stringifyed so we can see 
what's going on in the javascript console)
-----------------------------------------------------------------
*/
function update(){
    ddb.updateItem(params, function(err, data) {
        if (err) { return console.log(err); }
        console.log("We updated the table with this: " + JSON.stringify(data));
    });
}
/*
-----------------------------------------------------------------
function read()
Description: Calls getItem which is part of the AWS Javascript
SDK.
Returns: JSON object (the object is stringifyed so we can see 
what's going on in the javascript console)
-----------------------------------------------------------------
*/
function read(){
    ddb.getItem(readparams, function(err, data) {
        if (err) { return console.log(err); }
        console.log(": " + data);       

    console.log("John's favorite food is: "+ JSON.stringify(data.Item.food.S)); // print the item data
});
}

Answer 3

Below code is working for me, try once

 var item = {"endTime": "7pm", "imageName": "7abcd", "startTime": "7pm"};

dynamo.updateItem({
TableName:'tableName',
Key:{"primaryKey":"primaryKeyValue"},
AttributeUpdates: { images: { Action: "ADD", Value: item } }},function(err, data) {
    if (err)
        console.log(err);
    else
        console.log(data)
});