javascript 我可以有条件地向我的 knex 查询添加 where() 子句吗？
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Can I conditionally add a where() clause to my knex query?
提问by eponymous23
I want to add a where()clause in my query, but conditionally. Specifically, I want it added only if a sepecific querystring parameter is passed in the URL. Is this possible, and if so, how would I go about doing it?
我想where()在我的查询中添加一个子句，但有条件地. 具体来说，我希望只有在 URL 中传递了特定的查询字符串参数时才添加它。这是可能的，如果是这样，我将如何去做？
router.get('/questions', function (req, res) {
knex('questions')
.select('question', 'correct', 'incorrect')
.limit(50)
.where('somecolumn', req.query.param) // <-- only if param exists
.then(function (results) {
res.send(results);
});
});
采纳答案by Simon Briche
You can store your query in a variable, apply your conditional where clause and then execute it, like this :
您可以将查询存储在变量中，应用条件 where 子句然后执行它，如下所示：
router.get('/questions', function(req, res) {
var query = knex('questions')
.select('question', 'correct', 'incorrect')
.limit(50);
if(req.query.param == some_condition)
query.where('somecolumn', req.query.param) // <-- only if param exists
else
query.where('somecolumn', req.query.param2) // <-- for instance
query.then(function(results) {
//query success
res.send(results);
})
.then(null, function(err) {
//query fail
res.status(500).send(err);
});
});
回答by Itai Noam
Yes. Use modify.
是的。使用修改。
As applied to your example:
适用于您的示例：
router.get('/questions', function (req, res) {
knex('questions')
.select('question', 'correct', 'incorrect')
.limit(50)
.modify(function(queryBuilder) {
if (req.query.param) {
queryBuilder.where('somecolumn', req.query.param);
}
})
.then(function (results) {
res.send(results);
});
});
回答by Merey Nurlan
You can actually use query builder inside .where() like so:
您实际上可以在 .where() 中使用查询构建器，如下所示：
.where((qb) => {condition == true ? do something if true : do something if false })
IMO @ItaiNoam answer should be correct with .modify()
IMO @ItaiNoam 答案应该是正确的 .modify()
回答by Josh Lankford
You can do it by checking if your query string is present and running a different query.
您可以通过检查您的查询字符串是否存在并运行不同的查询来实现。
router.get('/questions', function(req, res) {
if (req.query.yourQueryString) {
// Run your more specific select
} else {
knex('questions').select('question', 'correct', 'incorrect').limit(50).where(
'somecolumn', req.query.param) // <-- only if param exists
.then(function(results) {
res.send(results);
});
}
}
});