Assert the projected SQL and fix the Mapperly sample in the docs

* RequiredMappingStrategy.Target avoids an RMG020 warning per unmapped entity property

docs/en/framework/architecture/domain-driven-design/application-services.md

@@ -485,13 +485,15 @@ public class BookProjector : IQueryProjectionMapper<Book, BookDto>
 [Mapperly](https://mapperly.riok.app/) can generate that method for you:
 
 ````csharp
-[Mapper]
+[Mapper(RequiredMappingStrategy = RequiredMappingStrategy.Target)]
 public partial class BookProjector : IQueryProjectionMapper<Book, BookDto>
 {
     public partial IQueryable<BookDto> ProjectTo(IQueryable<Book> source);
 }
 ````
 
+> `RequiredMappingStrategy.Target` tells Mapperly to only require the DTO members to be mapped. Without it, it reports a warning for every entity property that the DTO doesn't have.
+
 ABP registers the projection mappers by convention, you don't need to configure anything else. Filters (like soft delete and multi-tenancy), sorting and paging are still applied to the query before the projection.
 
 > The projection replaces the entity based extension points. `GetAsync` doesn't use `GetEntityByIdAsync` and `MapToGetOutputDtoAsync`, `GetListAsync` doesn't use `MapToGetListOutputDtosAsync` anymore. If an application service needs to keep using them, override the `GetProjectionMapper` or `GetListProjectionMapper` property and return `null`:

framework/test/Volo.Abp.EntityFrameworkCore.Tests/Volo/Abp/EntityFrameworkCore/Applications/QueryProjection_Tests.cs

@@ -1,9 +1,12 @@
 using System;
+using System.Linq;
 using System.Threading.Tasks;
+using Microsoft.EntityFrameworkCore;
 using Shouldly;
 using Volo.Abp.Application.Dtos;
 using Volo.Abp.Domain.Entities;
 using Volo.Abp.Domain.Repositories;
+using Volo.Abp.ObjectMapping;
 using Volo.Abp.TestApp;
 using Volo.Abp.TestApp.Domain;
 using Xunit;
@@ -63,4 +66,23 @@ public class QueryProjection_Tests : EntityFrameworkCoreTestBase
 
         result.Items.ShouldNotContain(x => x.Id == TestDataBuilder.UserJohnDeletedId);
     }
+
+    [Fact]
+    public async Task Should_Only_Select_The_Projected_Columns()
+    {
+        await WithUnitOfWorkAsync(async () =>
+        {
+            var repository = GetRequiredService<IReadOnlyRepository<Person, Guid>>();
+            var projector = GetRequiredService<IQueryProjectionMapper<Person, PersonProjectionDto>>();
+
+            var sql = projector.ProjectTo(await repository.GetQueryableAsync()).ToQueryString();
+
+            sql.ShouldContain("\"Name\"");
+            sql.ShouldNotContain("\"Birthday\"");
+            sql.ShouldNotContain("\"ExtraProperties\"");
+
+            //the data filters are still a part of the query
+            sql.ShouldContain("Is_Deleted");
+        });
+    }
 }

framework/test/Volo.Abp.Mapperly.Tests/Volo/Abp/Mapperly/SampleClasses/MyEntityQueryProjector.cs

@@ -4,7 +4,7 @@ using Volo.Abp.ObjectMapping;
 
 namespace Volo.Abp.Mapperly.SampleClasses;
 
-[Mapper]
+[Mapper(RequiredMappingStrategy = RequiredMappingStrategy.Target)]
 public partial class MyEntityQueryProjector : IQueryProjectionMapper<MyEntity, MyEntityDto>
 {
     public partial IQueryable<MyEntityDto> ProjectTo(IQueryable<MyEntity> source);