Mongo C# driver - Building filter dynamically with nesting

Question

Assume something like a nested expression

where a = 1 AND ( b = 4 OR b = 5 )

How to use multiple Builders objects and build a complete filter out of such an expression?

Is this a C# related problem? Do you want to build an expression dynamically? — Christo S. Christov
– Christo S. Christov, Commented Aug 26, 2015 at 13:12
I am sorry to keep the question incomplete. Yes, it's using C# driver 2.0 Builder classes. Yes, I want to build the expression into FilterDefinition dynamically. — Mr767267
– Mr767267, Commented Aug 27, 2015 at 4:35

rnofenko · Accepted Answer · 2020-12-22 02:37:35Z

147

Builders is really flexible class, it also has overridden operators "& = AND" and "| = OR"

Your example will be

var filter = Builders<User>.Filter.Eq(x => x.A, "1");
filter &= (Builders<User>.Filter.Eq(x => x.B, "4") | Builders<User>.Filter.Eq(x => x.B, "5"));

edited Dec 22, 2020 at 2:37

answered Aug 27, 2015 at 15:23

rnofenko

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6 Comments

Mr767267 Over a year ago

Thanks! I'll try to use this approach. The difficult part will be parsing the string based expression and building the nested FilterDefinition. Because when I parse the string into filter objects, I will go left to right and and will have to start with outer most builder and then navigate to child builders...may be I need some tree data structure

Igor Monteiro Over a year ago

best answer.. congrats!!

Brady Moritz Over a year ago

you'll definitely need to build a tree to do this correctly. Sounds like a fun project

Robert Smith Over a year ago

The other thing I'd consider here is that you don't need multiple builder objects. You can use the same builder for multiple filters.

nikolai.serdiuk Over a year ago

You can use: filter &= (Builders<User>.Filter.Eq(x => x.B, "4")

|

Ehsan Ehsani · Accepted Answer · 2021-06-27 19:56:18Z

27

if you want conditionally add more filters use this method:

var builder = Builders<Student>.Filter;
var filter = builder.Empty;

if (!string.IsNullOrWhiteSpace(firstName))
{
   var firstNameFilter = builder.Eq(x => x.FirstName, firstName);
   filter &= firstNameFilter;
}

if (!string.IsNullOrWhiteSpace(lastName))
{
   var lastNameFilter = builder.Eq(x => x.LastName, lastName);
   filter &= lastNameFilter;
}

if (minAge != null && maxAge != null)
{
   var ageFilter = builder.And(builder.Gt(x => x.Age, minAge),
      builder.Lt(x => x.Age, maxAge));
   filter &= ageFilter;
}

var result = await _plpResultCollection.Find(filter).ToListAsync();

answered Jun 27, 2021 at 19:56

Ehsan Ehsani

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2 Comments

Serve Laurijssen Over a year ago

thats what I came here for :)

Kaveh Naseri Over a year ago

This doesn't work if you use or (|=) expression, it will return all collections because of builder.empty

Rejwanul Reja · Accepted Answer · 2020-04-18 16:00:43Z

20

You can use very simply like this way.....

var filter = Builders<Rental>.Filter.Where(s => s._id== id && s.Price==1500);

answered Apr 18, 2020 at 16:00

Rejwanul Reja

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1 Comment

ejcortes Over a year ago

Although this doesn't answer the OPs question, it did help me on "my mission".

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