DynamoDB - Dynamically Build an Update Expression

update-example.js

const generateUpdateQuery = (fields) => {
    let exp = {
        UpdateExpression: 'set',
        ExpressionAttributeNames: {},
        ExpressionAttributeValues: {}
    }
    Object.entries(fields).forEach(([key, item]) => {
        exp.UpdateExpression += ` #${key} = :${key},`;
        exp.ExpressionAttributeNames[`#${key}`] = key;
        exp.ExpressionAttributeValues[`:${key}`] = item
    })
    exp.UpdateExpression = exp.UpdateExpression.slice(0, -1); 
    return exp
}

let data = {
    'field' : { 'subfield': 123 },
    'other': '456'
}

let expression = generateUpdateQuery(data)

let params = {
    // Key, Table, etc..
    ...expression
}

console.log(params)

This was useful. Thank you very much.
Added a python implementation of the same logic

def generate_update_query(fields):
    exp = {
        "UpdateExpression": 'set',
        "ExpressionAttributeNames": {},
        "ExpressionAttributeValues": {}
    }
    for key, value in fields.items():
        exp["UpdateExpression"] += f" #{key} = :{key},"
        exp["ExpressionAttributeNames"][f"#{key}"] = key
        exp["ExpressionAttributeValues"][f":{key}"] = value
    exp["UpdateExpression"] = exp["UpdateExpression"][0:-1] 
    return exp