Creating a dynamic LINQ statement without having an Entity Type Property
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06-07-2019 - |
Question
I'm trying to create a Linq statement that queries both columns that exist on my entity as properties and those that don't but exist as columns in the database for the entity.
For example, I have a collection of Book entities. Each Book has an ID and Title property and a matching column in the database. But, lets say the table for Book also contains a column field for Author and my Book entity doesn't have this.
A normal query involving the ID and the Title might look like this:
Books.Where(b=>b.ID == 123 && b.Title == "Title")
But, I want to also dynamically add the equivalent of " AND Author = 'Name' " to the above query as well. The Author property doesn't exist on the Book object.
The extra fields and the values they should contain will actually be available in a Dictionary. So I will need to dynamically add multiple AND [FieldName] = '[Value]' conditions to the query.
It might help explain why I would need this to know that I'm using Azure Table Storage and I have overridden the serialize that turns a Book entity into the XML stored in Azure.
Edit -
I've tried using the Dynamic Linq library but it does not work.
Books.Where(b=>b.ID == 123 && b.Title == "Title").Where("Author = @0", "SomeName").ToList();
Throws: System.Linq.Dynamic.ParseException: No property or field 'Author' exists in type 'Book'.
Also,
I know using Books.AddQueryOption("$filter","Author eq 'SomeName'") works when used by itself. But I have no idea how to use AddQueryOption along with an existing Where statement.
Solution 2
This is not possible with LINQ
OTHER TIPS
Without adding Author to Book, you would either have to pass another object with Author on it:
var x = new { Author="SomeName" };
Books.Where(b=>b.Id == 1 && b.Title == "Alpha").Where("@1.Author == @0", "SomeName", x);
Or inherit from Book and add an Author property just for this purpose:
public class BookEx : Book {
public string Author { get; set; }
}
Books.Cast<BookEx>().Where(b=>b.Id == 1 && b.Title== "Alpha").Where("Author == @0", "SomeName");
Have a look at the Dynamic Linq library.
Try the following code:
var result = _tofiObjectList.Where(o => o.GetType() == mainObjType)
.AsQueryable().Cast(relation.MainObject.EntityType).Where(relation.MainObject.Filter);
This is an extension method for IQueryable
type:
public static IQueryable Cast(this IQueryable source, string type)
{
switch (type)
{
case "TofiDataCollection.Service.TofiEntity.Obj":
return source.Cast<Obj>();
}
return source;
}