dynamodb item update doesn't support UpdateExpression (SET)

Documentation on UpdateExpression (SET):

http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.Modifying.html#Expressions.Modifying.UpdateExpressions.SET

Exception:

self = Item: {'Attributes': {'Hk': {'S': 'queue_name:0'}, 'Rk': {'S': '4I7CaHMQPNhhGkv_AyOCyP61QYZJETkyEccZletk'}}}
update_expression = 'SET MT = if_not_exists(MT, :message_type), MC = if_not_exists(MC, :message_content), SI = if_not_exists(SI, :sender_i...first_visible_time), RT = if_not_exists(RT, :minus_1), RC = if_not_exists(RC, :zero), DT = if_not_exists(DT, :minus_1)'
expression_attribute_names = {}
expression_attribute_values = {':first_visible_time': {'N': '63608879137.886993408203125'}, ':message_content': {'S': '$'}, ':message_type': {'S': '$type_0'}, ':minus_1': {'N': '-1'}, ...}

    def update(self, update_expression, expression_attribute_names, expression_attribute_values):
        ACTION_VALUES = ['SET', 'set', 'REMOVE', 'remove']

        action = None
        for value in update_expression.split():
            if value in ACTION_VALUES:
                # An action
                action = value
                continue
            else:
                # A Real value
                value = value.lstrip(":").rstrip(",")
            for k, v in expression_attribute_names.items():
                value = value.replace(k, v)
            if action == "REMOVE" or action == 'remove':
                self.attrs.pop(value, None)
            elif action == 'SET' or action == 'set':
>               key, value = value.split("=")
E               ValueError: need more than 1 value to unpack

Specifically, it’s having trouble parsing this:

SET MT = if_not_exists(MT, :message_type), MC = if_not_exists(MC, :message_content), SI = if_not_exists(SI, :sender_id), ST = if_not_exists(ST, :now), FV = if_not_exists(FV, :first_visible_time), NV = if_not_exists(NV, :first_visible_time), RT = if_not_exists(RT, :minus_1), RC = if_not_exists(RC, :zero), DT = if_not_exists(DT, :minus_1)

Hk is the hash key and Rk is the range key.

Sorry I haven’t written a simple test case that reproduces the error. I’m at work and I need to move on to other things.

I produced this error on commit ea319698aab8c8e1c6f55d4e115808c725bac268 of moto.

[ericman93]

trying to use list_append

 table.update_item(
    Key={
        'request_id': unique_id
    },
    ExpressionAttributeValues={':file_name': ['ABC']},
    UpdateExpression='SET file_names = list_append(file_names, :file_name)'
)

but when I query dynamo later the value of file_names is list_append(file_names, :file_name) same issue when i’m trying to increment value, the value after I query is the update expression

[ryansydnor]

Seeing the same issue. Looks like if_not_exists and list_append operations are not supported yet. Furthermore, after splitting on the = sign there’s a possibility for both the key and value to have spurious whitespace. I’d recommend trimming them.