The following code works for me if I need to filter a generic query for a single parameter, like Status=1.
public static IQueryable<T> FilterBy<T>(this IQueryable<T> query)
{
var propertyName = "Status";
var param_1 = "1";
//var param_2 = 2;
//var param_3 = "DE";
var parameterExp = Expression.Parameter(typeof(T), "type");
var propertyExp = Expression.Property(parameterExp, propertyName);
var converter = TypeDescriptor.GetConverter(propertyExp.Type);
var result = converter.ConvertFrom(param_1);
var value = Expression.Constant(result);
var equalBinaryExp = Expression.Equal(propertyExp, value);
query = query.Where(Expression.Lambda<Func<T, bool>>(equalBinaryExp, parameterExp));
return query;
}
This is like filtering a list with a value.
var list = new List<Employee> {
new Employee { Id = 1, Name = "Phil", Status=1, Country="DE" } ,
new Employee { Id = 2, Name = "Kristina", Status=2, Country="DE" },
new Employee { Id = 3, Name = "Mia", Status=1, Country="US" }
};
list = list.Where(x => (x.Status == 1)).ToList();
But how should I modify the method FilterBy, so that it will work for filtering multiple values? Like (Status=1 or Status=2) and Country="DE",
list = list.Where(x => (x.Status == 1 || x.Status == 2) && x.Country == "DE").ToList();
Thanks for your time.
The trick when writing lambdas by hand is to write them how you would in regular C#, and decompile them, perhaps using sharplab like this . If you look on the right, you can see that it is doing something like:
Expression.AndAlso(
Expression.OrElse(
Expression.Equal(idPropExp, Expression.Constant(1)),
Expression.Equal(idPropExp, Expression.Constant(2))
),
Expression.Equal(countryPropExp, Expression.Constant("DE"))
)
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