访问其他实体内部的实体方法获取对象引用错误

Question

我在里面有实体类和方法，如下所示

public class OpaqueConstruction :AEIMasterBase
{
public string Name { get; set; }
[Column(TypeName = "jsonb")]
public List<OpaqueMaterial> Layers { get; set; }
public Construction AddToOsm(Model model)
{
if (model is null)
{
throw new ArgumentNullException(nameof(model));
}
// code 
construction.setLayers(materials);
return construction;
}
public OpaqueConstruction() { }
}
public class ConstructionSet : AEIMaster
{
[ForeignKey("ExteriorWall"), GraphQLIgnore]
public Guid? ExteriorWallId { get; set; }
public virtual OpaqueConstruction ExteriorWall { get; set; }
public void AddToOsm(Model model)
{
if (model is null)
{
throw new ArgumentNullException(nameof(model));
}
using var constructionSet = new DefaultConstructionSet(model);
using var exteriorSurfaceConstructions = new DefaultSurfaceConstructions(model);
using var exteriorWall = this.ExteriorWall.AddToOsm(model); // getting error at here object reference set exception
exteriorSurfaceConstructions.setWallConstruction(exteriorWall);
}
public ConstructionSet () { }
}

我正试图通过导航属性从其他实体(如这里的this.ExteriorWall.AddToOsm(model)(访问在一个实体中编写的方法，并获得对象引用错误，但无法弄清楚，这些类是实际的实体，我正在使用EF核心和.net核心

请任何人告诉我上面的代码哪里出错了，非常感谢！！

Answer 1

无论何时查询ConstructionSet，都要像-一样包含ExteriorWall

var constructionSet = context.ConstructionSets.Include(p=> p.ExteriorWall).FirstOrDefault();

并且，当您调用ExteriorWall上的方法时，请执行null检查(下面的？运算符(，如-

var exteriorWall = this.ExteriorWall?.AddToOsm(model);

以防没有为您的ConstructionSet找到相关的OpaqueConstruction数据。