更新表达式updateExpression

主题：

SET - 修改或添加项目属性
REMOVE - 从项目中删除属性
ADD - 更新数字和集合
DELETE - 从集合中删除元素

set 修改属性

 case 'PUT': {var table = 'book_table', hash = 'book', id = "05d101be-d5e8-43ec-8eb6-5530e21af83e";var params = {TableName: table,Key: {"hash": hash,"id": id},   UpdateExpression: "SET #p = :p, #sn = :n, #c = #c + :c",ExpressionAttributeNames: {"#p": "price","#sn": "sn","#c": "count"},ExpressionAttributeValues: {":p": 100.99,":n": "100-100-010",":c": 1},
                ReturnValues: "UPDATED_NEW"};await docClient.update( params ).promise().then(( success ) => {response.body = JSON.stringify({ "success:": success })}).catch(( err ) => {console.log(err);response.statusCode = err.statusCode;response.body = JSON.stringify({code: err.code,message: err.message})});callback( null, response );break;};

　　程序运行成功返回如下：

{"success:": {"Attributes": {"count": 9,"price": 100.99,"sn": "100-100-010"}}
}

添加列表和映射

case 'POST': {var table = "book_table", hash = "book";var params = {TableName: table,
                Item: { "hash": hash,"id": uuid(),"booktype":['青春文学', '历史典故']}  };await docClient.put( params ).promise().then(( data ) => {response.body =  JSON.stringify({"success": data})}).catch(( err ) =>{response = {    statusCode: err.statusCode,body: JSON.stringify({code: err.code,message: err.message})}})callback( null, response );break;}

　　　　程序运行成功后返回：

{"success": {}
}

将元素添加到列表：

case 'PUT': {var table = 'book_table', hash = 'book', id = "bee1bea0-4b6a-4fbc-8cf0-8c030519c909";var params = {TableName: table,Key: {"hash": hash,"id": id},
UpdateExpression: "SET #type = list_append(#type, :t)",ExpressionAttributeNames: {"#type": "booktype"},ExpressionAttributeValues: {":t": ["读者杂志","最小说","科技畅想"]},};await docClient.put( params ).promise().then(( data ) => {response.body =  JSON.stringify({"success": data})}).catch(( err ) =>{response = {statusCode: err.statusCode,body: JSON.stringify({code: err.code,message: err.message})}})callback( null, response );break;}

　　程序运行成功后返回：

{"success:": {"Attributes": {"booktype": ["青春文学","历史典故","读者杂志","最小说","科技畅想",],"hash": "book","id": "556433cf-37b6-4e12-b513-9c261fd279f7"}}
}

添加嵌套映射属性

        case 'POST': {var table = "book_table", hash = "book";var params = {TableName: table,Item: { "hash": hash,"id": uuid(),
                    "type": {"list1": ["武侠小说", "社科图书"],"list2": ["儿童读物", "漫画书"],"list3": ["法律", "经济"]}
}};await docClient.put( params ).promise().then(( data ) => {response.body =  JSON.stringify({"success": data})}).catch(( err ) =>{response = {statusCode: err.statusCode,body: JSON.stringify({code: err.code,message: err.message})}})callback( null, response );break;}

case 'PUT': {var table = 'book_table', hash = 'book', id = "bee1bea0-4b6a-4fbc-8cf0-8c030519c909";var params = {TableName: table,Key: {"hash": hash,"id": id},
                UpdateExpression: "SET #t.#l1 = :b1, #t.#l3 = :b3",ExpressionAttributeNames: {"#t": "type","#l1": "list1","#l3": "list3"},ExpressionAttributeValues: {":b1": ["军事","艺术"],":b3": ["社会","科学"]},ReturnValues: "ALL_NEW"
            };await docClient.update( params ).promise().then(( success ) => {response.body = JSON.stringify({ "success:": success })}).catch(( err ) => {console.log(err);response.statusCode = err.statusCode;response.body = JSON.stringify({code: err.code,message: err.message})});callback( null, response );break;};

　　程序运行成功后返回：

{"success:": {"Attributes": {"type": {"list1": ["军事","艺术"],"list3": ["社会","科学"],"list2": ["儿童读物","漫画书"]},"hash": "book","id": "bee1bea0-4b6a-4fbc-8cf0-8c030519c909"}}
}

对数值属性进行加减（对现有数值属性执行加减运算。为此，请使用 +（加号）和 -（减号）运算符。）

case 'POST': {var table = "book_table", hash = "book";var params = {TableName: table,                Item: {"hash": hash,"id": uuid(),"name": "三重门","author": "韩寒","type": "情感其他","sn": "100-100-008","price": 103.50,"date": "2010-01-01","count": 7,"description": "本书通过少年林雨翔的视角，向读者揭示了真实的高中生的生活，体现了学生式的思考、困惑和梦想。"}
            };console.log( params.Item.count );await docClient.put( params ).promise().then(( data ) => {response.body =  JSON.stringify({"success": data})}).catch(( err ) =>{response = {statusCode: err.statusCode,body: JSON.stringify({code: err.code,message: err.message})}})callback( null, response );break;}

case 'PUT': {var table = 'book_table', hash = 'book', id = '4b99e00f-9f57-41f7-80de-d581e8c84522';var params = {TableName: table,Key: {"hash": hash,"id": id},                 UpdateExpression: "SET #p = :p, #sn = :n, #c = #c + :c",ExpressionAttributeNames: {"#p": "price","#sn": "sn","#c": "count"},ExpressionAttributeValues: {":p": 100.99,":n": "100-100-010",":c": 1},ReturnValues: "ALL_NEW"
            };await docClient.update( params ).promise().then(( success ) => {response.body = JSON.stringify({ "success:": success })}).catch(( err ) => {console.log(err);response.statusCode = err.statusCode;response.body = JSON.stringify({code: err.code,message: err.message})});callback( null, response );break;};

　　程序运行成功后返回：

{"success:": {"Attributes": {"date": "2010-01-01","author": "韩寒","price": 99.99,"count": 8,"name": "三重门","description": "本书通过少年林雨翔的视角，向读者揭示了真实的高中生的生活，体现了学生式的思考、困惑和梦想。","id": "4b99e00f-9f57-41f7-80de-d581e8c84522","sn": "100-100-100","type": "情感其他","hash": "book"}}
}

将元素附加到列表

     case 'PUT': {var table = 'book_table', hash = 'book', id = '4b99e00f-9f57-41f7-80de-d581e8c84522';var params = {TableName: table,Key: {"hash": hash,"id": id},                UpdateExpression: "SET #type = list_append(#type, :t)",ExpressionAttributeNames: {"#type": "booktype"},ExpressionAttributeValues: {":t": ["穿越时空", "玄幻小说"]},ReturnValues: "ALL_NEW"
            };await docClient.update( params ).promise().then(( success ) => {response.body = JSON.stringify({ "success:": success })}).catch(( err ) => {console.log(err);response.statusCode = err.statusCode;response.body = JSON.stringify({code: err.code,message: err.message})});callback( null, response );break;};

　　程序运行成功后返回：

{"success:": {"Attributes": {"booktype": ["青春文学","历史典故","读者杂志","最小说","科技畅想","穿越时空","玄幻小说"],"hash": "book","id": "556433cf-37b6-4e12-b513-9c261fd279f7"}}
}

防止覆盖现有属性（设置项目的 Price，但仅当项目还没有 Price 属性时设置。(如果 Price 已存在，则不执行任何操作。)）

 case 'PUT': {var table = 'book_table', hash = 'book', id = '4b99e00f-9f57-41f7-80de-d581e8c84522';var params = {TableName: table,Key: {"hash": hash,"id": id},  UpdateExpression: "SET price = if_not_exists(price, :p)",ExpressionAttributeValues: {":p": 100},
            ReturnValues: "ALL_NEW"};await docClient.update( params ).promise().then(( success ) => {response.body = JSON.stringify({ "success:": success })}).catch(( err ) => {console.log(err);response.statusCode = err.statusCode;response.body = JSON.stringify({code: err.code,message: err.message})});callback( null, response );break;};

　　程序运行成功后返回：

{"success:": {"Attributes": {"booktype": ["青春文学","历史典故","读者杂志","最小说","科技畅想","穿越时空","玄幻小说"],"id": "556433cf-37b6-4e12-b513-9c261fd279f7","price": 100,"hash": "book"}}
}

REMOVE：从项目中删除属性(如果属性不存在，则不会执行任何操作。)

ps: DELETE不存在 "ALL_NEW"或”UPDATED_NEW“的属性

 1  case 'PUT': {
 2
 3             var table = 'book_table', hash = 'book', id = '4b99e00f-9f57-41f7-80de-d581e8c84522';
 4
 5             var params = {
 6                 TableName: table,
 7                 Key: {
 8                     "hash": hash,
 9                     "id": id
10                 },
11
12                UpdateExpression: "REMOVE booktype[7]",
13             ReturnValues: "ALL_NEW"
14             };
15
16            await docClient.update( params ).promise().then(
17                 ( success ) => {
18                     response.body = JSON.stringify({ "success:": success })
19                 }
20
21             ).catch(
22                 ( err ) => {
23                     console.log(err);
24                     response.statusCode = err.statusCode;
25                     response.body = JSON.stringify({
26                         code: err.code,
27                         message: err.message
28                     })
29                 }
30             );
31             callback( null, response );
32             break;
33         };

　　程序运行成功后返回：

{"success:": {"Attributes": {"booktype": ["青春文学","历史典故","读者杂志","最小说","科技畅想","穿越时空",],"id": "556433cf-37b6-4e12-b513-9c261fd279f7","price": 100,"hash": "book"}}
}

　注： ALL_NEW 将导致 DynamoDB 按更新后的情况返回项目；UPDATED_NEW仅将DynamoDB 按更新后的部分情况返回项目。

本文为原创，还望指教！

若有疑问，可在下方留言，也可自读AWS官方文档——DynamoDB： https://docs.aws.amazon.com/zh_cn/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html

转载于:https://www.cnblogs.com/landen/p/9780768.html

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