Get value from Database to Linq where clause

Question

I have a table called FILTRE_LINKLER and column's names are

1. ID
2. SEF_URL
3. CONDITIONS

For example,

• ID=1
• SEF_URL="test/"
• CONDITIONS="STOCK>50"`

I want to get CONDITIONS part to linq where clause.

var product = (from d in db.PRODUCTS
                       where *CONDITIONS from DB*
                       select new ProductModel
                       {
                           Description= d.DESCRIPTION,
                           Brand= d.BRANDS.BRAND,
                           SefUrl = sef_url,
                           Name= d.NAME,

                       });

I try to that:

var query = db.FILTRE_LINKLER.Select(x => x.CONDITIONS);
 var product = (from d in db.PRODUCTS
                       where query
                       select new ProductModel
                       {
                           Description= d.DESCRIPTION,
                           Brand= d.BRANDS.BRAND,
                           SefUrl = sef_url,
                           Name= d.NAME,

                       });

But I have an error that is Cannot implicitly convert type 'System.Linq.IQueryable' to bool.

I edited because "Problem Solved". For solution:

Download Install-Package System.Linq.Dynamic -Version 1.0.7 (said me @StepUp) then add to class

using System.Linq.Dynamic;

then following code like that,

 var whereCondition = db.FILTRE_LINKLER.Select(x => x.CONDITIONS).FirstOrDefault();
var product = (from d in db.PRODUCTS
                       where query
                       select new ProductModel
                       {
                           Description= d.DESCRIPTION,
                           Brand= d.BRANDS.BRAND,
                           SefUrl = sef_url,
                           Name= d.NAME,

                       }).Where(whereCondition);

Answer 1

Try to use Dynamic LINQ. This is a sample of code using Dynamic LINQ library:

var query = northwind.Products
                         .Where("CategoryID = 3 AND UnitPrice > 3")
                         .OrderBy("SupplierID");

In your case:

var whereCondition = db.FILTRE_LINKLER.Select(x => x.CONDITIONS).FirstOrDefault();
var product = (from d in db.PRODUCTS
                   select new ProductModel
                   {
                       Description= d.DESCRIPTION,
                       Brand= d.BRANDS.BRAND,
                       SefUrl = sef_url,
                       Name= d.NAME,

                   })
              .Where(whereCondition);

UPDATE:

1. At first you should download a code to use Dynamic queries by this link.

2. Then use DynamicQueryable class from the project Dynamic Query

3. Then use your dynamic queries with IQueryable<T>.

Let me show an example:

var persons = new List<Person>()
{
    new Person(){Id = 1, FirstName = "1"},
    new Person(){Id = 2, FirstName = "2"},
    new Person(){Id = 3, FirstName = "3"}
};
var personWithIdTwo = persons
   .AsQueryable()
   .Where("Id==2");

UPDATE 1:

If you do not want to add class, then you can use an Expression Tree.

An example of an expression tree:

var propName = "STOCK"; // here you assign any value
var constValue = "50";  // here you assign any value
var param = Expression.Parameter(typeof(ProductModel), "p");
var exp = Expression.Lambda<Func<ProductModel, bool>>(
    Expression.GreaterThan(
       Expression.Property(param, propName),
       Expression.Constant(constValue)
    ),
    param
);
var product = (from d in db.PRODUCTS
                   where query
                   select new ProductModel
                   {
                       Description= d.DESCRIPTION,
                       Brand= d.BRANDS.BRAND,
                       SefUrl = sef_url,
                       Name= d.NAME,

                   }).Where(exp);

UPDATE 2:

You can download library Dynamic query through NuGet. So you should not create classes in your project: