我是这项技术的新手。所以请忍受我下面的解释。
我的用例:
我正在基于主键(ID)更新Dynamodb中的项目。基本上我的记录有4列(ID,描述,名称,价格)。
这里的问题是假设我有一个钥匙为123的物品
ID description name price
123 Model nokia 10
当我使用上述lamda函数更新所有列时,它工作正常。
但是,当我尝试仅更新description
列时,会抛出“ ExpressionAttributeValues不能为空”的错误。因此,我做了这样的事情
ExpressionAttributeValues:{
":d":event.description ? event.description : null ,
":n":event.name ? event.name : null,
":p":event.price ? event.price : null
}
但是问题是它将更新我给定的唯一值。
就像如果我只给description
赋予modal1
一样,它将改变它并给出这样的结果
ID description name price
123 Model1 null null
这是正确的,因为上面的代码片段表示可以这样做。
我想实现什么?
我如何将这种行为更改为达到这种目的
ID description name price
123 Model1 nokia 10
感谢您的帮助
更新的代码
var AWS = require("aws-sdk");
AWS.config.update({
region: "regionname",
endpoint: "endpointurl"
});
var docClient = new AWS.DynamoDB.DocumentClient()
var tablename = "Example";
var UpdateExpression = "'set";
var ExpressionAttributeValues= {};
var ExpressionAttributeNames= {};
var ID = "xx";
var description = "Iphone";
var name = "xx";
var price = 50;
var params = {
TableName: tablename,
Key:{
"ID": ID
}
};
docClient.update(params,onUpdate);
function onUpdate(err) {
if (err) {
console.error("Unable to scan the table. Error JSON:", JSON.stringify(err, null, 2));
} else {
console.log("Update succeeded.");
}
if(description) {
UpdateExpression = UpdateExpression + " description = :d,",
ExpressionAttributeValues [":d"] = description ,
console.log("first...")
}
if(name){
UpdateExpression = UpdateExpression + " #na = :n,",
ExpressionAttributeNames['#na'] = 'name' ,
ExpressionAttributeValues[":n"] = name ,
console.log("second...")
}
if(price){
UpdateExpression = UpdateExpression + " price = :p',",
ExpressionAttributeValues[":p"] = price ,
console.log("third...")
}
console.log(UpdateExpression)
console.log(ExpressionAttributeNames)
console.log(ExpressionAttributeValues)
return (UpdateExpression,ExpressionAttributeNames,ExpressionAttributeValues)
}
运行代码时,我得到这样的输出:
D:\ Dynamo>节点FullUpdate.js
Update succeeded.
first...
second...
third...
'set description = :d, #na = :n, price = :p',
{ '#na': 'name' }
{ ':d': 'Iphone', ':n': 'xx', ':p': 50 }
答案 0 :(得分:1)
您必须根据所拥有的变量来构造查询,因此您必须执行类似的操作
UpdateExpression = "set";
ExpressionAttributeValues: {};
ExpressionAttributeNames: {};
if(event.description){
UpdateExpression = UpdateExpression + "description = :d";
ExpressionAttributeValues[":d"] = event.description
}
if(event.name){
UpdateExpression = UpdateExpression + "#na = :n";
ExpressionAttributeNames['#na'] = 'name'
ExpressionAttributeValues[":d"] = event.name
}
if(event.price){
UpdateExpression = UpdateExpression + "price = :p";
ExpressionAttributeValues[":d"] = event.pice
}
请小心逗号,并记录查询以确保它符合您的期望。 您可以检查我为此目的使用的功能
update(_id, store_id, opts?) {
var Key = {
_id: _id,
store_id: store_id
};
if (Object.keys(opts).length > 0) {
let UpdateExpression =
"SET #date = :date, #author = :author";
let ExpressionAttributeNames = {
"#date": "date",
"#author": "author"
}
let ExpressionAttributeValues = {
":date": new Date().getTime(),
":author": localStorage.getItem('user_id')
}
if ((opts && opts.title)) {
UpdateExpression = UpdateExpression + "#title = :title,";
ExpressionAttributeNames["#title"] = "title";
ExpressionAttributeValues[":title"] = opts.title
}
if ((opts && opts.category)) {
UpdateExpression = UpdateExpression + "#category = :category,";
ExpressionAttributeNames["#category"] = "category";
ExpressionAttributeValues[":category"] = opts.category
}
if ((opts && opts.category)) {
UpdateExpression = UpdateExpression + "#dimension = :dimension,";
ExpressionAttributeNames["#dimension"] = "dimension";
ExpressionAttributeValues[":dimension"] = opts.dimension
}
if ((opts && opts.category)) {
UpdateExpression = UpdateExpression + "#destination = :destination,";
ExpressionAttributeNames["#destination"] = "destination";
ExpressionAttributeValues[":destination"] = opts.destination
}
if ((opts && opts.category)) {
UpdateExpression = UpdateExpression + "#timeStart = :timeStart,";
ExpressionAttributeNames["#timeStart"] = "timeStart";
ExpressionAttributeValues[":timeStart"] = opts.timeStart
}
if ((opts && opts.category)) {
UpdateExpression = UpdateExpression + "#timeEnd = :timeEnd,";
ExpressionAttributeNames["#timeEnd"] = "timeEnd";
ExpressionAttributeValues[":timeEnd"] = opts.timeEnd
}
if ((opts && opts.publish)) {
UpdateExpression = UpdateExpression + "#publish = :publish,"
ExpressionAttributeNames["#publish"] = "publish"
ExpressionAttributeValues[":publish"] = "x";
}
UpdateExpression = UpdateExpression.replace(new RegExp(',$'), '');
if ((opts && opts.nbviews)) {
UpdateExpression = UpdateExpression + "ADD #nbviews = :nbviews"
ExpressionAttributeNames["#nbviews"] = "nbviews"
ExpressionAttributeValues[":nbviews"] = 1;
}
if ((opts && !opts.publish)) {
UpdateExpression = UpdateExpression + " REMOVE #publish"
ExpressionAttributeNames["#publish"] = "publish"
}
return this.dataService.update(TABLENAME, Key, UpdateExpression, null, ExpressionAttributeNames, ExpressionAttributeValues);