打字稿链接承诺 [英] Typescript chaining Promises
问题描述
如果有人可以帮助解决以下打字稿错误,我将不胜感激.
谢谢.
我正在使用以下代码它有以下内容.它需要能够链接Promise
.
line 26: dbPromise = _db.execute(sql)
当我尝试构建它时,我得到以下信息:
<块引用> ./app/pages/chats/SqlDatabase.ts 中的错误(26,9): 错误 TS2322: 类型 'Promise'不可分配到类型Promise".类型 'SqlResultSet' 不能分配给类型 'SqlDatabase'.SqlResultSet"类型中缺少属性_db".
我使用的是 Typescript 2.0.3 版.
代码:
import { isBrowser } from './platform';从 './SqlResultSet' 导入 { SqlResultSet };导出类 SqlDatabase {构造函数(私有_db:任何){}static open(name: string, initStatements: string[] = []): Promise{让 dbPromise = isBrowser().then(浏览器 => {const openDatabase = 浏览器?openBrowserDatabase : openCordovaDatabase;返回 openDatabase(name);});如果(initStatements.length === 0){返回 dbPromise;}让 _db: SqlDatabase;//执行第一条语句并捕获_dbdbPromise.then(db => {_db = db;返回 db.execute(initStatements.shift());});//依次执行所有其他语句(如果有)for (let sql of initStatements) {dbPromise.then(() => {dbPromise = _db.execute(sql)});}//只有在所有语句完成后才解析 _db返回新的承诺((解决,拒绝)=> {console.log('resolve: ', resolve);dbPromise.then(() => resolve(_db)).catch(reject);});}execute(statement: string, params: any[] = []): Promise{console.log('执行:' + 语句);返回新的承诺((解决,拒绝)=> {this._db.transaction(tx => tx.executeSql(statement, params, (tx, resultSet) => {console.log('执行:解析:',resultSet);解决(结果集);}, (tx, error) =>{拒绝(错误)}));});}}声明 var sqlitePlugin: any;函数 openCordovaDatabase(name: string): Promise{返回新的承诺((解决,拒绝)=> {if (typeof sqlitePlugin === '未定义') {拒绝(新错误('[ionix-sqlite] sqlitePlugin 全局对象未找到;您是否安装了 Cordova SQLite 插件?'));}const db = sqlitePlugin.openDatabase({姓名:姓名,位置:'默认'});console.info('[ionix-sqlite] 使用 Cordova sqlitePlugin');解决(新的SqlDatabase(db));});}声明函数 openDatabase(name: string, version: string, desc: string, size: number): any;函数 openBrowserDatabase(name: string): Promise{返回新的承诺((解决,拒绝)=> {尝试 {const db = openDatabase(name, '1.0', name, -1);console.info('[ionix-sqlite] 使用 WebSQL');解决(新的SqlDatabase(db));} 捕捉(错误){拒绝(错误);}});}
错误是由于您尝试更改 dbPromise
的类型.
首次声明时:
let dbPromise = isBrowser().then(浏览器 => {const openDatabase = 浏览器?openBrowserDatabase : openCordovaDatabase;返回 openDatabase(name);});
编译器将类型引用到 Promise
(基于错误),但随后您尝试分配其他内容:
dbPromise = _db.execute(sql)
属于 Promise
类型.
你可以这样解决:
let dbPromise: Promise= ...
或者你可以有两个不同的 promise 变量(即:dbPromise:Promise
和 resultPromise:Promise
),这对我来说听起来更好.>
If anyone can help with the following Typescript Error, I would appreciate it.
Thanks.
I am making use of the following code where it has the following. It needs to be able to chain the Promise
.
line 26: dbPromise = _db.execute(sql)
When I try build it, I get the following:
ERROR in ./app/pages/chats/SqlDatabase.ts (26,9): error TS2322: Type 'Promise<SqlResultSet>' is not assignable to type 'Promise<SqlDatabase>'. Type 'SqlResultSet' is not assignable to type 'SqlDatabase'. Property '_db' is missing in type 'SqlResultSet'.
I am using Typescript version 2.0.3.
code:
import { isBrowser } from './platform';
import { SqlResultSet } from './SqlResultSet';
export class SqlDatabase {
constructor(private _db: any) { }
static open(name: string, initStatements: string[] = []): Promise<SqlDatabase> {
let dbPromise = isBrowser()
.then(browser => {
const openDatabase = browser ? openBrowserDatabase : openCordovaDatabase;
return openDatabase(name);
});
if (initStatements.length === 0) {
return dbPromise;
}
let _db: SqlDatabase;
// execute the first statement and capture the _db
dbPromise.then(db => {
_db = db;
return db.execute(initStatements.shift());
});
// execute all the other statements (if any) sequentially
for (let sql of initStatements) {
dbPromise.then(() => {
dbPromise = _db.execute(sql)
});
}
// resolve the _db only after all statements have completed
return new Promise((resolve, reject) => {
console.log('resolve: ', resolve);
dbPromise.then(() => resolve(_db)).catch(reject);
});
}
execute(statement: string, params: any[] = []): Promise<SqlResultSet> {
console.log('execute: ' + statement);
return new Promise((resolve, reject) => {
this._db.transaction(tx => tx.executeSql(statement, params, (tx, resultSet) => {
console.log('execute: resolve: ', resultSet);
resolve(resultSet);
}, (tx, error) => {
reject(error)
}));
});
}
}
declare var sqlitePlugin: any;
function openCordovaDatabase(name: string): Promise<SqlDatabase> {
return new Promise((resolve, reject) => {
if (typeof sqlitePlugin === 'undefined') {
reject(new Error('[ionix-sqlite] sqlitePlugin global object not found; did you install a Cordova SQLite plugin?'));
}
const db = sqlitePlugin.openDatabase({
name: name,
location: 'default'
});
console.info('[ionix-sqlite] using Cordova sqlitePlugin');
resolve(new SqlDatabase(db));
});
}
declare function openDatabase(name: string, version: string, desc: string, size: number): any;
function openBrowserDatabase(name: string): Promise<SqlDatabase> {
return new Promise((resolve, reject) => {
try {
const db = openDatabase(name, '1.0', name, -1);
console.info('[ionix-sqlite] using WebSQL');
resolve(new SqlDatabase(db));
} catch (error) {
reject(error);
}
});
}
The error is due to the fact that you try to change the type of dbPromise
.
When it is first declared:
let dbPromise = isBrowser()
.then(browser => {
const openDatabase = browser ? openBrowserDatabase : openCordovaDatabase;
return openDatabase(name);
});
the compiler refers the type to Promise<SqlDatabase>
(based on the error), but then you try to assign something else:
dbPromise = _db.execute(sql)
which is of type Promise<SqlResultSet>
.
You can solve it like so:
let dbPromise: Promise<any> = ...
Or you can have two different promise variables (i.e.: dbPromise: Promise<SqlDatabase>
and resultPromise: Promise<SqlResultSet>
) which sounds better to me.
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