DynamoDB : SET list_append not working using aws sdk
Solution 1
list_append
can be read as a "concatenate" operation. You just give it two lists.
"UpdateExpression" : "SET #attrName = list_append(#attrName, :attrValue)",
"ExpressionAttributeNames" : {
"#attrName" : "entries"
},
"ExpressionAttributeValues" : {
":attrValue" : ["000989"]
}
It's worth remembering that lists (and maps) in DynamoDB are not typed and can store arbitrary data.
Side note: Armed with this knowledge, the documentation on appending to the beginning of the list now makes sense:
list_append (operand, operand)
This function evaluates to a list with a new element added to it. You can append the new element to the start or the end of the list by reversing the order of the operands.
Solution 2
There's an accepted answer on this question which helped me with part of this issue. However, we'll typically want to update lists with additional objects, not strings. For this, I found it useful to avoid using ExpressionAttributeNames if possible.
1) Make sure the value in your item in your DynamoDB table is a list. 2) Make sure you pass in a list of objects (even if you only have one), not a simple object
UpdateExpression: "set pObj.cObj= list_append(pObj.cObj, :obj)",
ExpressionAttributeValues: {
":obj": [
{myObject: {
property1: '',
property2: '',
property3: '',
}}
]
},
Solution 3
I thought I'd just throw this out there as another option for adding or appending an "object" to a list. It's a map being added an item to the list, and worked well for me:
var upsertExpr = (obj.comments == undefined) ? " :attrValue" : "list_append(#attrName, :attrValue)";
var params = {
TableName: 'tableName',
Key: {
'id': {'S': id},
},
UpdateExpression : "SET #attrName = " + upsertExpr,
ExpressionAttributeNames : {
"#attrName" : "comments"
},
ExpressionAttributeValues : {
":attrValue" : {
"L": [
{ "M" :
{
"comment": {"S": comment},
"vote": {"N": vote.toString()}
}
}
]
}
}
};
Solution 4
maybe this will help someone. i was struggling with updating a list and was getting the same error message as the original poster. i managed to solve my problem when i finally understood the documentation (see the Adding Elements To a List example here http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.ADD)
points to note are: 1) that the "list_append takes two lists as input, and appends the second list to the first." and 2) that ExpressionAttributeValues is a list! like this:
{
":vals": {
"L": [
{ "S": "Screwdriver" },
{"S": "Hacksaw" }
]
}
}
good luck!
![void](https://i.stack.imgur.com/6eeyM.jpg?s=256&g=1)
Comments
-
void over 3 years
I need to append a string to a string set in a dynamodb table using the corresponding key. This is the Update expression I use to do updateItem :
var params = { "TableName" : tableName, "Key": { "ID": { S: "20000" } }, "UpdateExpression" : "SET #attrName = list_append(#attrName, :attrValue)", "ExpressionAttributeNames" : { "#attrName" : "entries" }, "ExpressionAttributeValues" : { ":attrValue" : {"SS":["000989"]} } };
This works when I do updateItem() using the aws cli. But when using aws-sdk in nodejs, I am getting the error:
Invalid UpdateExpression: Incorrect operand type for operator or function; operator or function: list_append, operand type: M\n
Any help? Thanks
-
samcorcos over 7 yearsThat did it for me, thanks. The important thing to note is that list_append takes in two lists:
list_append([list1], [list2])
. Anything else will error. So if you pass an object/map (as I was attempting to do), you need to wrap that object in a list: [{ object }] -
CuriousCoder over 7 yearsThanks a lot for this answer. Been searching how to update lists with objects for so long
-
djf over 5 yearsThank you so much! I've been trying to figure this out for two days. Unfortunately, the AWS documentation only covers the most trivial use cases..
-
Steven Musumeche over 2 yearsThe key is that the object you are adding has to be wrapped in a list itself. Thank you.
-
Rafael Bertelli about 2 yearsThanks! that did it