实体框架-实体查找不抛出无参数构造函数

Question

I have the "Find" method throwing this exception when executed: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: The class 'NWatch.Entities.NWatchConvertMethod' has no parameterless constructor.

Adding the ConvertMethod to the dbContext and saving changes has no problems.

Code:

[TestMethod]
        public void Delete()
        {
            // Add the entry
            var convertMethod = RenderConvertMethod();
            dbContext.ConvertMethods.Add(convertMethod);
            dbContext.SaveChanges();
            int id = convertMethod.ConvertMethodId;

            // Remove entry
            dbContext.ConvertMethods.Remove(convertMethod);
            dbContext.SaveChanges();

            // Ensure the entry no longer exists in the DB
            // BELOW LINES THROWS THE EXCEPTION
            var convertMethodFromDb = dbContext.ConvertMethods.Find(id);
            Assert.IsNull(convertMethodFromDb);
        }

        private NWatchConvertMethod RenderConvertMethod()
        {
            var convertMethod = new NWatchConvertMethod("TestConvertMethod")
            {
                ConvertMethodDesc = "my description"
            };

            return convertMethod;
        }

Answer 1

All entities must have a parameterless constructor. It can be private if you want:

http://social.technet.microsoft.com/wiki/contents/articles/3820.entity-framework-faq-entity-classes.aspx#Does_the_Entity_Framework_require_objects_with_public_empty_constructors

You must add a parameterless constructor to NWatchConvertMethod.