On a previous post we proceeded into inserting items to DynamoDB using Node.js. DynamoDB also supports updating items.
We will use the Login table for the update examples.
When issuing an update you must specify the primary key of the item you want to update.
var updateName = function(email,fullName,callback) {
var docClient = new AWS.DynamoDB.DocumentClient();
var params = {
TableName:"Users",
Key: {
email : email
},
UpdateExpression: "set fullname = :fullname",
ExpressionAttributeValues:{
":fullname":fullName
},
ReturnValues:"UPDATED_NEW"
};
docClient.update(params,callback);
}We can proceed on more advanced statements using conditional updates. Conditional updates can help us in many cases such as handling concurrent updates. In our case we will update an item’s Full name only if it starts with a certain prefix.
var updateConditionally = function(email,fullName,prefix,callback) {
var docClient = new AWS.DynamoDB.DocumentClient();
var params = {
TableName:"Users",
Key: {
email : email
},
UpdateExpression: "set fullname = :fullname",
ConditionExpression: "begins_with(fullname,:prefix)",
ExpressionAttributeValues:{
":fullname":fullName,
":prefix":prefix
},
ReturnValues:"UPDATED_NEW"
};
docClient.update(params,callback);
}Another feature is atomic counters. We can issue updates to a DynamoDB item and increase the attribute values. We will add an extra field called count. Also we will add another update function, which once called will update the field specified, but will also increase the counter attribute. Thus the counter attribute will represent how many times an update was performed on a specific item.
var addUpdateCounter = function(email,callback) {
var docClient = new AWS.DynamoDB.DocumentClient();
var params = {
TableName:"Users",
Key: {
email : email
},
UpdateExpression: "set #counter = :counter",
ExpressionAttributeNames:{
"#counter":"counter"
},
ExpressionAttributeValues:{
":counter":0
},
ReturnValues:"UPDATED_NEW"
};
docClient.update(params,callback);
}
var updateAndIncreaseCounter = function(email,fullName,callback) {
var docClient = new AWS.DynamoDB.DocumentClient();
var params = {
TableName:"Users",
Key: {
email : email
},
UpdateExpression: "set fullname = :fullname ADD #counter :incva",
ExpressionAttributeNames:{
"#counter":"counter"
},
ExpressionAttributeValues:{
":fullname":fullName,
":incva":1
},
ReturnValues:"UPDATED_NEW"
};
docClient.update(params,callback);
}You can find the sourcecode on github.
| Reference: | Update DynamoDB Items with Node.js from our WCG partner Emmanouil Gkatziouras at the gkatzioura blog. |
