dbro.many("SELECT geoname_id,country_name FROM paises WHERE locale_code=$1 LIMIT 10",data.lang) .then(function(countriesData){ data.countries=countriesData; dbro.many("SELECT * FROM categorias") .then(function(categoriesData){ data.categories=(categoriesData) console.log(data); res.render('layout',data); res.end(); }) .catch(function(err){ console.log("error while fetching categories data"); }) }) .catch(function(err){ console.log("error while fetching countries data",err); });
不知怎的,我认为这是不对的.如果我需要在返回回调之前获得许多查询的结果,该怎么办?几个then / catch的嵌套变得丑陋.目标是在呈现页面之前准备好所有数据(在Express中)
解决方法
初始化
const pgp = require('pg-promise')(/* initialization options */); const db = pgp('postgres://username:password@host:port/database');
db.task('get-user-events',t => { return t.one('select * from users where id = $1',123) .then(user => { return t.any('select * from events where login = $1',user.name); }); }) .then(data => { // data = result from the last query; }) .catch(error => { // error });
当查询没有依赖关系时,我们应该在任务中将它们作为batch执行:
db.task('get-everything',t => { return t.batch([ t.any('select * from users'),t.one('select count(*) from events') ]); }) .then(data => { // data[0] = result from the first query; // data[1] = result from the second query; }) .catch(error => { // error });
请注意,我强调每个语句都带有“should”,因为您可以执行任务或事务之外的所有内容,但由于管理数据库连接的方式,因此不建议这样做.
当您需要为每个HTTP请求执行单个查询时,您应该只对根协议(db对象)执行查询.应始终在任务/事务中执行多个查询.
另见Chaining Queries,其主要点位于底部:
If you do not follow the advised approach,your application will perform better under a small load,due to more connections allocated in parallel,but under a heavy load it will quickly deplete the connection pool,crippling performance and scalability of your application.
UPDATE
从pg-promise v7.0.0开始,我们可以在一个命令中从多个查询中提取结果,这比以前的所有解决方案都高效得多:
db.multi('SELECT * FROM users;SELECT count(*) FROM events') .then(data => { // data[0] = result from the first query; // data[1] = result from the second query; }) .catch(error => { // error });
或者,如果您使用的是Bluebird,那么:
db.multi('SELECT * FROM users;SELECT count(*) FROM events') .spread((users,[{count}]) => { // users = array of user records; // count = string with the count; }) .catch(error => { // error });
请参阅新方法multi和multiResult.
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