Question

当我运行这行代码时

queryCompanies =（DbSet）queryCompanies.Include（path）;

从这个方法：

     public Company GetCompanyById(int companyId)
     {
        List<string> includePaths = new List<string>();
        includePaths.Add("Addresses");
        includePaths.Add("Users");
        Company company = null;
        using (Entities dbContext = new Entities())
        {   
            var queryCompanies = dbContext.Companies;

            if (includePaths != null)
            {
                foreach (string path in includePaths)
                    queryCompanies = (DbSet<Company>)queryCompanies.Include(path);
            }

                company = (from c in queryCompanies
                           where c.Id.Equals(companyId)
                           select c).FirstOrDefault<Company>();
        }
        return company;
     }

我收到此错误：

无法转换类型为'System.Data.Entity.Infrastructure.DbQuery 1[ClassLibrary1.Company]' to type 'System.Data.Entity.DbSet 1 [ClassLibrary1.Company]'的对象。

编译时我没有错误。在EF 4.0中，此代码运行正确，而不是使用DbSet＆lt;＆gt;，ObjectQuery＆lt;＆gt;。

我是EF 4.1的初学者，所以任何建议都会有用。

感谢。

Answer 1

试试这个

 public Company GetCompanyById(int companyId)
 {
    List<string> includePaths = new List<string>();
    includePaths.Add("Addresses");
    includePaths.Add("Users");
    Company company = null;
    using (Entities dbContext = new Entities())
    {   
        var queryCompanies = dbContext.Companies.AsQueryable();

        if (includePaths != null)
        {
            foreach (string path in includePaths)
                queryCompanies = queryCompanies.Include(path);
        }

            company = (from c in queryCompanies
                       where c.Id.Equals(companyId)
                       select c).FirstOrDefault<Company>();
    }
    return company;
 }

Answer 2

DbSet继承自DbQuery，因此编译器不会抱怨，因为强制转换可能有效。显然，DbSet<T>.Include返回的不是DbSet<T>，并且演员在运行时失败。

但是，你不需要施放;调用FirstOrDefault将适用于DbQuery<T>。

Answer 3

我写了一个通用的包含检查器方法。现在这不好，但这是工作。我会重构这个。也许它符合你的需求。

    List<TEntityType> GetEntityListTemplate(Expression<Func<TEntityType, bool>> expression = null)
    {
        List<TEntityType> entityList;
        DbQuery<TEntityType> query = null;

        Type entityType = typeof(TEntityType);
        PropertyInfo[] properties = entityType.GetProperties();

        using (DatabaseContext database = new DatabaseContext())
        {
            database.Database.Connection.Open();

            foreach (PropertyInfo property in properties)
            {
                if (property.PropertyType.FullName.Contains("Your.Identifier.Namespace"))
                {
                    if (query == null)
                    {
                        query = database.Set<TEntityType>().Include(property.Name);
                    }
                    else
                    {
                        query = query.Include(property.Name);
                    }
                }
            }

            if (query == null)
            {
                if (expression == null)
                {
                    entityList = database.Set<TEntityType>().ToList();
                }
                else
                {
                    entityList = database.Set<TEntityType>().Where(expression).ToList();
                }
            }
            else //(query!=null)
            {
                if (expression == null)
                {
                    entityList = query.ToList();
                }
                else
                {
                    entityList = query.Where(expression).ToList();
                }
            }
        }

        return entityList;
    }

C＃Entity Framework 4.1：在查询中包含用于加载相关对象的路径

3 个答案: