Question

我正在使用 nodejs和postgresqlDB 开发一个项目。我想做的是，设置一个带有一些表的架构，这些表中也有彼此的外键。我实际解决方案中的问题是，每次启动应用程序时查询的顺序都不同。所以当它来的时候attributeTable是在架构之前创建的，从逻辑上讲是错误的。但是如何保存查询的顺序，以便按我想要的顺序创建表和架构？

我试图将相关表放在.then子句中，但是效果不佳。

        function getDB(callback) {
            let pgp = require('pg-promise')({
                // Initialization Options
            });

           // fetches uri for queries       
           var dbPostgres = pgp(returnUriToDB());

           // sql-queries in some constants
           let createSchema = createSchema;
           let attributeTable = createAttributeTable;
           let objectGroupTable = createObjectGroupTable;

           dbPostgres.query(createSchema)
                    .then(function () {
                        console.log('+++++ schema exists or was successfully created');
                        return;
                    })
                    .catch((err) => {
                        console.log(err);
                        console.log('----- schema could not be initialized :(');
                        return;
                    });

           dbPostgres.query(attributeTable)
                    .then(function () {
                        console.log('+++++ attributeTable exists or was successfully created');
                        return;
                    })
                    .catch((err) => {
                        console.log(err);
                        console.log('attributeTable could not be initialized :(');
                        return;
                    });

           dbPostgres.query(objectGroupTable)
                    .then(function () {
                        console.log('+++++ objectGroupTable exists or was successfully created');
                        return;
                    })
                    .catch((err) => {
                        console.log(err);
                        console.log('----- objectGroupTable could not be created :(');
                        return;
                    }); 
}

Answer 1

这些调用dbPostgres.query是异步的。检查承诺。

dbPostgres.query(createSchema)
    .then(function() {
        console.log('+++++ schema exists or was successfully created');
        return;
    })
    .catch((err) => {
        console.log(err);
        console.log('----- schema could not be initialized :(');
        return;
    })
    .then(dbPostgres.query(attributeTable))
    .then(function() {
        console.log('+++++ attributeTable exists or was successfully created');
        return;
    })
    .catch((err) => {
        console.log(err);
        console.log('attributeTable could not be initialized :(');
        return;
    })
    .then(dbPostgres.query(objectGroupTable))
    .then(function() {
        console.log('+++++ objectGroupTable exists or was successfully created');
        return;
    })
    .catch((err) => {
        console.log(err);
        console.log('----- objectGroupTable could not be created :(');
        return;
    });

使用等待（更具可读性）

async function whatever() {
    await dbPostgres.query(createSchema).catch((err) => {
        console.log(err);
        console.log('----- schema could not be initialized :(');
    });
    console.log('+++++ schema exists or was successfully created');

    await dbPostgres.query(attributeTable).catch((err) => {
        console.log(err);
        console.log('attributeTable could not be initialized :(');
    });
    console.log('+++++ attributeTable exists or was successfully created');

    await dbPostgres.query(objectGroupTable).catch((err) => {
        console.log(err);
        console.log('----- objectGroupTable could not be created :(');
        return;
    });
    console.log('+++++ objectGroupTable exists or was successfully created');

}

// you can use async functions like promises (with then-catch schema)

whatever.then(..).catch(..).then(..);

使用Node.js为Postgresql创建多个数据库表

1 个答案: