How to avoid manual inlining inside LINQ query to use as an expression and convert to SQL

I am trying to do some projections in LINQ to convert to DTOs. The goal is to do it with expressions so that it is translated directly to SQL.

It works perfectly if I do everything inlined like this :

 return workHeader.Select(x => new WorkHeaderDto
            {
                Id = x.Id,
                StartDate = x.Works.Min(w => w.StartDate),
                EndDate = x.Works.Min(w => w.EndDate),
                Parcelles = x.Works.SelectMany(w => w.Parcelles).Distinct(),
                Tools = x.Works.SelectMany(w => w.Tools).Select(t => t.Tool).Distinct().OrderBy(t => t.ToolId).AsQueryable().Select(t => new ToolDto
                {
                    RankNumber = t.RankNumber,
                    Comments = t.Comments,
                    OrderNumber = t.OrderNumber,
                    Garage = t.Garage,
                    Maintained = t.Maintained,
                    OI = t.OI,
                })
            }
        );

This way the projection is actually done in SQL, selecting only the needed columns from Tool.

But I want the mapping code to be reusable, so I first tried to put it inside a static method in another file and use it like this :

 return workHeader.Select(x => new WorkHeaderDto
            {
                Id = x.Id,
                StartDate = x.Works.Min(w => w.StartDate),
                EndDate = x.Works.Min(w => w.EndDate),
                Parcelles = x.Works.SelectMany(w => w.Parcelles).Distinct(),
                Tools = x.Works.SelectMany(w => w.Tools).Select(t => t.Tool).Distinct().OrderBy(t => t.ToolId).AsQueryable().Select(t => DtoMapper.ToDto(t))
            }
        );

But when I do this it is not considered an expression for some reasons, and the SQL query will load all fields from tools and do the mapping in memory.

So I’ve tried the following :

static Expression<Func<Tool, ToolDto>> ConvertExpression = t1 => new ToolDto
    {
        RankNumber = t.RankNumber,
        Comments = t.Comments,
        OrderNumber = t.OrderNumber,
        Garage = t.Garage,
        Maintained = t.Maintained,
        OI = t.OI,
    };

 return workHeader.Select(x => new WorkHeaderDto
            {
                Id = x.Id,
                StartDate = x.Works.Min(w => w.StartDate),
                EndDate = x.Works.Min(w => w.EndDate),
                Parcelles = x.Works.SelectMany(w => w.Parcelles).Distinct(),
                Tools = x.Works.SelectMany(w => w.Tools).Select(t => t.Tool).Distinct().OrderBy(t => t.ToolId).AsQueryable().Select(ConvertExpression)
            }
        );

But now the request doesn’t work at all. Do note that it is used by HotChocolate for a GraphQL query.

It works perfectly when inlined (projection in SQL and the good result), not perfectly when calling a method (projection in memory with full select in SQL, but good result) and not at all with the expression (graphql returns an error).

What is the best way to reuse the mapping code but keep doing the projection in sql ?