How can I convert lambda expression with C#?

Question

I need IQueryable extension method for my custom query. Example method and I want be result is below. How can I do this ?

Input =>

.Where(x => x.Id == 1)
.FilterContent<ProductTranslate>(x => x.ProductName == "product1" 
                                      && x.ShortDescription.Contains("short desc") 
                                      || x.Description.Contains("desc"), 1)

Output=>

x => (x.Key == "ProductName" && x.Value=="product1")
     && (x.Key == "ShortDescription" && x.Value.Contains("short desc") 
         || (x.Key == "Description" && x.Value.Contains("desc")))

Regards.

Answer 1

I think I understand what you are asking, but I will say the solution is way beyond me.

It sounds like to me that you need a function that parses an expression tree of type Func<Product, bool> (or more generally Func<T, TResult>) and convert it into an expression tree of type Func<ProductTranslate, bool> (or more generally Func<T2, TResult>).

The article https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/expression-trees/how-to-modify-expression-trees may be a start. The translation function would walk the original tree and build up a new modified tree. Luckily, it looks like ExpressionVisitor base class can do most of the work. You would need check each node to see if it is a T.Property reference and replace it with the appropriate T2.Property, T2["Property"], T2.GetPropertyValueByName("Property") or similar. You may also have to identify and replace whatever node accepts this T and an input parameter and replace it with a this T2 equivalent. Tracking the Product ID and language ID may involve additional changes.

As to how to detect and interpret the T.Property node, that may take some digging on your part, but I expect there must be some tools out there to dump expression trees in human readable forms that could help. Perhaps you can dump an original expression tree and a hand-coded objective expression tree to examine the differences.

If you get through all that, applying the new function to the IQueryable<>.Where() function should be the easy part.

P.S., Out of interest, is the following roughly the database structure you are working with, where your ProductTranslateKey class is your in-memory on-demand loaded representation of LanguageTranslate?

Products:

ID	ProductName	ShortDescription	Description
1	Water	Water is good	Water is very good
2	Fire	Fire is bad	Fire is very bad

Languages:

ID	Code	Description
1	EN	English
2	DE	Deutsch
3	FR	français

LanguageTranslate:

ProductID	LanguageId	Key	Value
1	1	ProductName	Water
1	1	ShortDescription	Water is good
1	1	Description	Water is very good
1	2	ProductName	Wasser
1	2	ShortDescription	Wasser ist gut
1	2	Description	Wasser ist sehr gut
1	3	ProductName	Leau
1	3	ShortDescription	Leau est bonne
1	3	Description	Leau est très bonne
2	1	ProductName	Fire
2	1	ShortDescription	Fire is bad
2	1	Description	Fire is very bad
2	2	ProductName	Feuer
2	2	ShortDescription	Feuer ist schlecht
2	2	Description	Feuer ist sehr schlecht
2	3	ProductName	Feu
2	3	ShortDescription	Le feu est mauvais
2	3	Description	Le feu est très mauvais

Answer 2

My rough database scheme is below. I have a TranslateRecords and TranslateResource tables for covers all entities multilanguage content. I put the translateId column with multiple language options entity table. So I can use all my content in one table without opening a separate translate table for each entity.

I just want to make an extension method because very complex queries occur in the filters I mentioned in the topic.

I will take your suggestions into consideration.