Custom Expression for a Property

Sometimes one of your property can be used for filtering multiple properties of something special. So you can create your own attributes to make custom expression for your custom queries. Following entity models will be used in this document:

• Blog.cs

pulic class Blog
{
    public string BlogId { get; set; }
    public int CategoryId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public bool IsPublished { get; set; }
    public virtual ICollection<Comment> Comments { get; set; }
    public virtual Author Author { get; set; } 
}

Attributes

You can create your own attributes for your custom expression requirements. Create a class which inherits FilteringOptionsBaseAttribute class and override abstract methods. Let's make a sample. For example our Search property will search in Blog Title and Content.

• Create your filtering dto:

public class SearchDto : FilterBase
{
    [FromQuery(Name = "q")]
    public string Search { get; set; }
}

• Then Create an attribute something like that:

 public class BlogSearchAttribute : FilteringOptionsBaseAttribute
    {
        public override Expression BuildExpression(Expression expressionBody, PropertyInfo targetProperty, PropertyInfo filterProperty, object value)
        {
            // Also means:  x => x.Title == "someValue" || x.Content == "someValue"
            return Expression.Or(
                    Expression.Equal(
                        Expression.Property(expressionBody, "Title"),
                        Expression.Constant(value)
                        ),
                    Expression.Equal(
                        Expression.Property(expressionBody, "Content"),
                        Expression.Constant(value)
                        )
                );
        }
    }

• Then go and place your attribute over your property:

public class SearchDto : FilterBase
{
    [FromQuery(Name = "q")]
    [BlogSearchAttribute] // <-- Place here
    public string Search { get; set; }
}

Types

You can create your own type with own expression generation like Range object. Just create your class, inherit and implement IFilterableType interface. Autfilterer will use your implemented BuildExpression() method.