C# Dynamic Linq Variable Where clause

Question

I am following Scott Gu's article to create a dynamic LINQ http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

He has given an example:

Expression<Func<Customer, bool>> e1 = 
    DynamicExpression.ParseLambda<Customer, bool>("City = \"London\"");  
Expression<Func<Customer, bool>> e2 =
    DynamicExpression.ParseLambda<Customer, bool>("Orders.Count >= 10");  
IQueryable<Customer> query =
    db.Customers.Where("@0(it) and @1(it)", e1, e2);

This works fine in my case. However I have unknown number of where clauses, which is decided at runtime.

Can anyone please tell me how to create a generic Where clause, such as

Where("@0(it) and @1(it) and... @n(it)", e1, e2, ... en);

Thanks

How about trying with something like db.Customers.Where( c => c.Order.Count > someVariable1 && c.Order.Count < someVariable2 ); — HatSoft
– HatSoft, Commented Jun 25, 2012 at 13:20

Wiktor Zychla · Accepted Answer · 2012-06-25 13:00:15Z

19

You can attach additional operators on the query object:

 query = db.Customers.Where( ... );
 query = query.Where( ... );
 query = query.Where( ... );

This way you can attach clauses dynamically and you are independent on their count.

answered Jun 25, 2012 at 13:00

Wiktor Zychla

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2 Comments

gunnerz Over a year ago

Thanks Thats what I am doing now

Neo Over a year ago

how to do IN clause in where?

SysAdmin · Accepted Answer · 2022-09-26 05:43:11Z

0

I have created a nuget package called DynamicFilter.Sql to achieve exactly this. For my requirement, I wanted to generate LINQ expression trees from sql syntax.

Here is how you would use it in your case.

var filter = FilterExpression.Compile<Customer>("City = 'London' and OrderCount >= 10");

//Filter a collection
var filteredCustomers = customers.Where(filter);

The package can generate code for complex logical/boolean operations and support sql style filtering including like, not like, in, not in, is null, is not null etc.

The package is open source and available on github, in case you would like to check the internals.

answered Sep 26, 2022 at 5:43

SysAdmin

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