Promise - return 数据通过 async / await 函数保持不变
Promise - return data to constant with async / await function
我正在尝试理解 knex 并为其创建了以下示例服务层：
const config = require('../db/knexfile');
const env = 'development';
const knex = require('knex')(config[env]);
/**
* Return all posts
*/
function getAllPosts() {
return knex('posts').select().then(data => {
return data
})
}
/**
* Create a post
*/
function create(title, description) {
console.log("Titel: " + title + " Description: " + description)
return knex('posts')
.insert({
title: title,
description: description,
deleted: true,
createdAt: new Date(),
updatedAt: new Date()
}, 'id')
.then(id => {
console.log("Inserted post with id "+ id)
return id;
})
.catch((err) => console.log(err));
}
/**
* find a post by id
*/
function findById(id) {
try {
return knex('posts').select().where('id', id).first().then(data => {
return data
})
} catch (e) {
console.log(e)
}
}
module.exports = {
create,
getAllPosts,
findById
}
我正在从另一个文件调用上面的文件：
const service = require('./t5_0-serviceLayer')
async function main() {
//prepare data
//service.prepareData()
//getAll
service.getAllPosts().then(data => {
console.log(JSON.stringify(data))
})
//create
const id = service.create("Test post", "Test description")
console.log("Post with " + id + ": " + service.findById(id))
//get all Posts
const res = service.getAllPosts()
console.log("We have " + res.length + " posts.")
}
main().then().catch(err => console.error(err))
我得到以下输出：
Titel: Test post Description: Test description
Post with undefined undefined
We have undefined posts.
[{"id":43,"title":"Et saepe qui occaecati unde nesciunt et.","description":"Sint commodi possimus sunt voluptatibus rerum. Incidunt mollitia accusantium ita
que nihil tempora. Qui veritatis ipsam expedita velit aut consequatur distinctio. Veritatis culpa labore rem ut a non perferendis.","deleted":false,"created
At":"2017-09-17T03:18:19.452Z","updatedAt":"2017-09-17T06:29:40.385Z","deletedAt":"2017-09-17T08:05:17.367Z"},{"id":44,"title":"Deserunt laborum reiciendis
magnam doloremque animi aspernatur sunt quod.","description":"Ea recusandae voluptas magni magni ipsum non dolorem iusto modi. Ipsum fuga inventore corporis
qui. Qui voluptatum eaque nesciunt expedita sed ipsa vel dolor inventore. Quos praesentium dolorum aut et amet amet tempora sed et.","deleted":true,"create
dAt":"2017-09-16T22:23:51.956Z","updatedAt":"2017-09-17T13:46:44.679Z","deletedAt":"2017-09-17T11:09:14.936Z"},{"id":45,"title":"Quibusdam sunt qui beatae."
,"description":"Aut tempore totam. Nihil qui est rerum ut ipsum at autem sint. Pariatur tempore praesentium. Magnam doloremque ipsam. Nihil nesciunt odit bl
anditiis.","deleted":false,"createdAt":"2017-09-16T20:58:03.889Z","updatedAt":"2017-09-17T11:19:06.696Z","deletedAt":"2017-09-17T03:42:25.541Z"},{"id":46,"t
itle":"Test post","description":"Test description","deleted":true,"createdAt":"2017-09-17T17:34:12.882Z","updatedAt":"2017-09-17T17:34:12.882Z","deletedAt":
null},{"id":47,"title":"Test post","description":"Test description","deleted":true,"createdAt":"2017-09-17T17:35:54.056Z","updatedAt":"2017-09-17T17:35:54.0
56Z","deletedAt":null},{"id":48,"title":"Test post","description":"Test description","deleted":true,"createdAt":"2017-09-17T17:36:28.801Z","updatedAt":"2017
-09-17T17:36:28.801Z","deletedAt":null}]
Unhandled rejection Error: Undefined binding(s) detected when compiling FIRST query: select * from "posts" where "id" = ? limit ?
at QueryCompiler_PG.toSQL (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\knex\lib\query\compiler.js:131:13)
at Builder.toSQL (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\knex\lib\query\builder.js:115:44)
at C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\knex\lib\runner.js:56:32
at tryCatcher (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\util.js:16:23)
at C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\using.js:185:26
at tryCatcher (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\util.js:16:23)
at Promise._settlePromiseFromHandler (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:512:31)
at Promise._settlePromise (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:569:18)
at Promise._settlePromise0 (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:614:10)
at Promise._settlePromises (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:693:18)
at Promise._fulfill (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:638:18)
at PromiseArray._resolve (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise_array.js:126:19)
at PromiseArray._promiseFulfilled (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise_array.js:144:14)
at Promise._settlePromise (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:574:26)
at Promise._settlePromise0 (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:614:10)
at Promise._settlePromises (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:693:18)
Inserted post with id 49
我目前的服务层存在以下问题
- 当我调用
const id = service.create("Test post", "Test description") 时，我没有得到创建的 post 的 ID
- 当我调用
service.getAllPosts() 时，我没有得到 post 的长度
对我做错了什么有什么建议吗？
service.getAllPosts()returns一个承诺，不是承诺的价值。所以这显然不是您期望的数组。
您需要继续使用 then 才能访问只能异步使用的结果：
service.getAllPosts().then(function(res) {
console.log("We have " + res.length + " posts.");
});
您似乎在 main 函数上使用了 async。您需要在 main 中的每个承诺返回函数调用之前放置 await。我假设 service.create returns 一个承诺？如果是这样，那么使用这样的东西：
const id = await service.create("Test post", "Test description")
service.getAllPosts也是如此：
const res = await service.getAllPosts()
@trincot 的回答没有错...它只是忽略了您正在尝试使用 async 的事实，这是现代节点版本上可用的语言功能。参见：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function
请记住，您可能希望在 try/catch 块中执行此操作以处理任何意外错误。
我正在尝试理解 knex 并为其创建了以下示例服务层：
const config = require('../db/knexfile');
const env = 'development';
const knex = require('knex')(config[env]);
/**
* Return all posts
*/
function getAllPosts() {
return knex('posts').select().then(data => {
return data
})
}
/**
* Create a post
*/
function create(title, description) {
console.log("Titel: " + title + " Description: " + description)
return knex('posts')
.insert({
title: title,
description: description,
deleted: true,
createdAt: new Date(),
updatedAt: new Date()
}, 'id')
.then(id => {
console.log("Inserted post with id "+ id)
return id;
})
.catch((err) => console.log(err));
}
/**
* find a post by id
*/
function findById(id) {
try {
return knex('posts').select().where('id', id).first().then(data => {
return data
})
} catch (e) {
console.log(e)
}
}
module.exports = {
create,
getAllPosts,
findById
}
我正在从另一个文件调用上面的文件：
const service = require('./t5_0-serviceLayer')
async function main() {
//prepare data
//service.prepareData()
//getAll
service.getAllPosts().then(data => {
console.log(JSON.stringify(data))
})
//create
const id = service.create("Test post", "Test description")
console.log("Post with " + id + ": " + service.findById(id))
//get all Posts
const res = service.getAllPosts()
console.log("We have " + res.length + " posts.")
}
main().then().catch(err => console.error(err))
我得到以下输出：
Titel: Test post Description: Test description
Post with undefined undefined
We have undefined posts.
[{"id":43,"title":"Et saepe qui occaecati unde nesciunt et.","description":"Sint commodi possimus sunt voluptatibus rerum. Incidunt mollitia accusantium ita
que nihil tempora. Qui veritatis ipsam expedita velit aut consequatur distinctio. Veritatis culpa labore rem ut a non perferendis.","deleted":false,"created
At":"2017-09-17T03:18:19.452Z","updatedAt":"2017-09-17T06:29:40.385Z","deletedAt":"2017-09-17T08:05:17.367Z"},{"id":44,"title":"Deserunt laborum reiciendis
magnam doloremque animi aspernatur sunt quod.","description":"Ea recusandae voluptas magni magni ipsum non dolorem iusto modi. Ipsum fuga inventore corporis
qui. Qui voluptatum eaque nesciunt expedita sed ipsa vel dolor inventore. Quos praesentium dolorum aut et amet amet tempora sed et.","deleted":true,"create
dAt":"2017-09-16T22:23:51.956Z","updatedAt":"2017-09-17T13:46:44.679Z","deletedAt":"2017-09-17T11:09:14.936Z"},{"id":45,"title":"Quibusdam sunt qui beatae."
,"description":"Aut tempore totam. Nihil qui est rerum ut ipsum at autem sint. Pariatur tempore praesentium. Magnam doloremque ipsam. Nihil nesciunt odit bl
anditiis.","deleted":false,"createdAt":"2017-09-16T20:58:03.889Z","updatedAt":"2017-09-17T11:19:06.696Z","deletedAt":"2017-09-17T03:42:25.541Z"},{"id":46,"t
itle":"Test post","description":"Test description","deleted":true,"createdAt":"2017-09-17T17:34:12.882Z","updatedAt":"2017-09-17T17:34:12.882Z","deletedAt":
null},{"id":47,"title":"Test post","description":"Test description","deleted":true,"createdAt":"2017-09-17T17:35:54.056Z","updatedAt":"2017-09-17T17:35:54.0
56Z","deletedAt":null},{"id":48,"title":"Test post","description":"Test description","deleted":true,"createdAt":"2017-09-17T17:36:28.801Z","updatedAt":"2017
-09-17T17:36:28.801Z","deletedAt":null}]
Unhandled rejection Error: Undefined binding(s) detected when compiling FIRST query: select * from "posts" where "id" = ? limit ?
at QueryCompiler_PG.toSQL (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\knex\lib\query\compiler.js:131:13)
at Builder.toSQL (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\knex\lib\query\builder.js:115:44)
at C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\knex\lib\runner.js:56:32
at tryCatcher (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\util.js:16:23)
at C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\using.js:185:26
at tryCatcher (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\util.js:16:23)
at Promise._settlePromiseFromHandler (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:512:31)
at Promise._settlePromise (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:569:18)
at Promise._settlePromise0 (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:614:10)
at Promise._settlePromises (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:693:18)
at Promise._fulfill (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:638:18)
at PromiseArray._resolve (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise_array.js:126:19)
at PromiseArray._promiseFulfilled (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise_array.js:144:14)
at Promise._settlePromise (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:574:26)
at Promise._settlePromise0 (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:614:10)
at Promise._settlePromises (C:\Users\user\Desktop\Coding Projects\learning_knex\node_modules\bluebird\js\release\promise.js:693:18)
Inserted post with id 49
我目前的服务层存在以下问题
- 当我调用
const id = service.create("Test post", "Test description") 时，我没有得到创建的 post 的 ID
- 当我调用
service.getAllPosts() 时，我没有得到 post 的长度
对我做错了什么有什么建议吗？
service.getAllPosts()returns一个承诺，不是承诺的价值。所以这显然不是您期望的数组。
您需要继续使用 then 才能访问只能异步使用的结果：
service.getAllPosts().then(function(res) {
console.log("We have " + res.length + " posts.");
});
您似乎在 main 函数上使用了 async。您需要在 main 中的每个承诺返回函数调用之前放置 await。我假设 service.create returns 一个承诺？如果是这样，那么使用这样的东西：
const id = await service.create("Test post", "Test description")
service.getAllPosts也是如此：
const res = await service.getAllPosts()
@trincot 的回答没有错...它只是忽略了您正在尝试使用 async 的事实，这是现代节点版本上可用的语言功能。参见：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function
请记住，您可能希望在 try/catch 块中执行此操作以处理任何意外错误。