How to build a conditional query in Mongoose?

Question

The following code works with no querystrings or one querystring only. In other words, simply going to /characters returns all characters. But if you were to specify a querystring parameter /characters?gender=male it will return only male characters.

How could I extend this to work with either 1, 2, 3, or no querystrings? I would really prefer to avoid writing 8 or 9 different if-statements for each case. I was hoping Mongoose would simply ignore a $where clause if it's null or undefined, but that is not the case (see commented out code).

  var gender = req.query.gender;
  var race = req.query.race;
  var bloodline = req.query.bloodline;

  var query = Character.find();

  if (gender)
    query = query.where('gender').equals(gender);
  if (race)
    query = query.where('race').equals(race);
  if (bloodline)
    query = query.where('bloodline').equals(bloodline);

  /*
  query
    .where('gender').equals(new RegExp('^' + gender + '$', 'i'))
    .where('race').equals(new RegExp('^' + race + '$', 'i'))
    .where('bloodline').equals(new RegExp('^' + bloodline + '$', 'i'));
  */

  query.exec(function(err, characters) {
    if (err) throw err;
    res.send(characters);
  });

Edit: Well I guess I could do it with 7 if-statements for now. Unless someone finds a more elegant solution.

Edit 2:

Thanks guys. It's difficult to pick one answer because both of you have helped me to achieve this concise solution. Here is the entire thing now.

var conditions = {};

for (var key in req.query) {
  if (req.query.hasOwnProperty(key)) {
    conditions[key] = new RegExp('^' + req.query[key] + '$', 'i');
  }
}

var query = Character.find(conditions);
query.exec(function(err, characters) {
  if (err) throw err;
  res.send({ characters: characters });
});

No problem, but you should pick an answer for future users to know which helped you more. If you can't, think about writing your own answer and checking that one as correct. — cschaeffler
– cschaeffler, Commented Oct 30, 2013 at 21:31
You should remove your Edit 2 and write your own answer, that is great btw — Preview
– Preview, Commented Jul 28, 2014 at 9:21
Very nice - works great; except for the sanitation part with the RegEx which produces odd queries. — Cloudscape
– Cloudscape, Commented Feb 23, 2015 at 14:37

0rvidal · Accepted Answer · 2013-10-30 22:14:00Z

13

You don't need to call Query#where repeatedly, since you can pass all the conditions to Mongoose Model#find as:

var filteredQuery = {},
  acceptableFields = ['gender', 'race', /* etc */ ];

acceptableFields.forEach(function(field) {
  req.query[field] && filteredQuery[field] = req.query[field];
});

var query = Character.find(filteredQuery);

You'll also want to sanitize req.query depending on the allowed parameters you have in mind.

edited Oct 30, 2013 at 22:14

answered Oct 30, 2013 at 21:00

0rvidal

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Comments

Wolfdog · Accepted Answer · 2019-07-01 13:46:07Z

5

I am using destructing of objects for this task.

const filter = req.query.filter ? { _id: { $in: req.query.filter.split(',') } } : {};
const category = req.query.category ? { category: req.query.category } : {};
// more variables that you need and are empty objects if don't exist

const all = await Post.find({ ...filter, ...category }).exec();

answered Jul 1, 2019 at 13:46

Wolfdog

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Comments

cschaeffler · Accepted Answer · 2013-10-30 21:05:41Z

2

Well,

I would recommend something like this:

var query = Character.find()
if(req.params.length < 0) {
  for(var key in req.params) {
    query.where(req.params[key]).equals(key);
  }
} else {
  // do something without query params
}

this is not tested by me but it should work (maybe you need to modify it a bit but you get the idea). This solution is all about not checking what actually is in the params so be sure only good stuff comes in or validate it somewhere in the for loop, but would require some regex or if statements.

Hope this helps you.

answered Oct 30, 2013 at 21:05

cschaeffler

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1 Comment

Sahat Yalkabov Over a year ago

To future visitors: Accepted answer's example does not work. I am not even using req.params, but rather req.query. Instead of chaining .where, I am building a condition object dynamically and then pass it to Character.find(). Refer to my Edit #2.

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