Generated mappers and required attributes

[EniacMlezi]

When using the c#11.0 required feature, the generated mappers fail. Editinh Sample.CodeGen for example:

public class Person
{
    public required int ID { get; set; }
    public string LastName { get; set; }
    public string FirstMidName { get; set; }
}

And looking at the generated StudentMapper:

[stormaref]

@andrerav should we remove this part entirely and just generate the part with initialization values?
@EniacMlezi can you mention the complete source code, please

[andrerav]

@stormaref That is tempting, but it will change a lot of code for a lot of people. I think a similar solution to the one in #545 is preferable.

[stormaref]

@andrerav that fix won't work with this problem because in that case, the problem was setting the init-only property, and this line was ok:

_UserDto result = p4 ?? new _UserDto();

but in this case, the problem occurs on this line:

Person result = p4 ?? new Person();

and that solution won't fix this problem

[EniacMlezi]

@EniacMlezi can you mention the complete source code, please

The complete source code is the codegen sample in this repository (Sample.CodeGen), but with Person.Id made required and the C# langver set to support required.

[EniacMlezi]

Check this: for code sample: EniacMlezi@3840103

[leetal]

Has anyone found a solution to this?

[DocSvartz]

@andrerav
This part of the code is generated by NullPropagation. Improvement should be done there.

[DocSvartz]

@andrerav @leetal This is what you need, right?

.Lambda #Lambda1<System.Func`3[Mapster.Tests.Person554,Mapster.Tests.Person554,Mapster.Tests.Person554]>(
    Mapster.Tests.Person554 $var1,
    Mapster.Tests.Person554 $var2) {
    .Block(Mapster.Tests.Person554 $result) {
        .If ($var1 == null) {
            .Return #Label1 { null }
        } .Else {
            .Default(System.Void)
        };
        $result = ($var2 ?? .New Mapster.Tests.Person554(){
            ID = $var1.ID   // generate this only for the required property
        });
        .Block() {
            $result.ID = $var1.ID;
            $result.LastName = $var1.LastName;
            $result.FirstMidName = $var1.FirstMidName
        };
        .Return #Label1 { $result };
        .Label
            null
        .LabelTarget #Label1:
    }
}

[leetal]

Essentially, yes :) But I fear that it might not work if using for example different classes and say that the required property would be non-existent (in your var1 above) by having custom DTOs with mapping configs as an example, then that would not work right? What would be a “sensible default” in those cases without having a way to actually populate the required field somehow? Or am I completely wrong? 🤔

[DocSvartz]

If you use configuration. Then it will work too.

var source = new Person553 {  FirstMidName = "John", LastName = "Dow" }; // not Id
var destination = new Person554 { ID = 245, FirstMidName = "Mary", LastName = "Dow" };

TypeAdapterConfig<Person553, Person554>.NewConfig()
    .Map(dest => dest.ID, source => 0);

.Lambda #Lambda1<System.Func`3[Mapster.Tests.Person553,Mapster.Tests.Person554,Mapster.Tests.Person554]>(
    Mapster.Tests.Person553 $var1,
    Mapster.Tests.Person554 $var2) {
    .Block(Mapster.Tests.Person554 $result) {
        .If ($var1 == null) {
            .Return #Label1 { null }
        } .Else {
            .Default(System.Void)
        };
        $result = ($var2 ?? .New Mapster.Tests.Person554(){
            ID = 0
        });
        .Block() {
            $result.ID = 0;
            $result.LastName = $var1.LastName;
            $result.FirstMidName = $var1.FirstMidName
        };
        .Return #Label1 { $result };
        .Label
            null
        .LabelTarget #Label1:
    }
}

Without configuration, yes, it will not work.
But can try to add the ability to set a default value for the type :)

[DocSvartz]

With this configuration, the result will be correct. (not work on 7.4.0)

var source = new Person553 {  FirstMidName = "John", LastName = "Dow" };
var destination = new Person554 { ID = 245, FirstMidName = "Mary", LastName = "Dow" };

TypeAdapterConfig<Person553, Person554>.NewConfig()
    .Map(dest => dest.ID, source => 0)
    .Ignore(x=>x.ID);

.Lambda #Lambda1<System.Func`3[Mapster.Tests.Person553,Mapster.Tests.Person554,Mapster.Tests.Person554]>(
    Mapster.Tests.Person553 $var1,
    Mapster.Tests.Person554 $var2) {
    .Block(Mapster.Tests.Person554 $result) {
        .If ($var1 == null) {
            .Return #Label1 { null }
        } .Else {
            .Default(System.Void)
        };
        $result = ($var2 ?? .New Mapster.Tests.Person554(){
            ID = 0
        });
        .Block() {
            // id  is not modified  
            $result.LastName = $var1.LastName;              // update from source (var1)
            $result.FirstMidName = $var1.FirstMidName // update from source (var1)
        };
        .Return #Label1 { $result };
        .Label
            null
        .LabelTarget #Label1:
    }
}

[DocSvartz]

@andrerav I opened a PR that I hope adds this improvement. ))
But additional test samples or testing within the Prerelease are needed.