在集合中获取 Class 个实例 - EF Code First Fluent API

Question

我有以下三个类

Om_MembershipCharges Class

public class Om_MembershipCharges
{
    [Key]
    public Int32 MembershipChargesID { get; set; }
    public Decimal Amount { get; set; }
    public Int16 PerMonth { get; set; }
    public Int16? CountryID { get; set; }
    public Int16 MemebershipTypeID { get; set; }



    public virtual Om_MembershipType MemebershipType { get; set; }
    public virtual Om_Country Country { get; set; }
}

Om_MembershipType Class

public class Om_MembershipType
{
    [Key]
    public Int16 MemebershipTypeID { get; set; }
    public String MemebershipType { get; set; }
    public Boolean IsDefaultMembership { get; set; }

    public virtual ICollection<Om_MembershipCharges> MembershipCharges { get; set; }
}

Om_Country Class

public class Om_Country
{
    [Key]
    public Int16 CountryID { get; set; }
    public String CountryName { get; set; }
    public Boolean IsActive { get; set; }

    public Int16? CurrencyID { get; set; }
    public Int32? MembershipChargesID { get; set; }

    public virtual Om_Currency Currency { get; set; }
    public Om_MembershipCharges MembershipCharges { get; set; }

}

以下是我使用 Om_MembershipType Class 中的 MembershipCharges Property 获取所有会员费用的方法。我正在使用 Include 来获取集合。

public async Task<KeyValuePair<String, Om_MembershipType>> ListByMType(String mType)
{
    try
    {
        using (var membershipChargesContext = new DatabaseTables())
        {
            using (var transaction = new TransactionScope(
                TransactionScopeOption.Required,
                new TransactionOptions { IsolationLevel = IsolationLevel.ReadUncommitted },
                TransactionScopeAsyncFlowOption.Enabled))
            {
                membershipChargesContext.Configuration.ProxyCreationEnabled = false;
                var data = await membershipChargesContext
                    .tblMembershipType
                    .Where(i => i.MemebershipType == membershipType)
                    .Include(i => i.MembershipCharges)
                    .FirstOrDefaultAsync();
                transaction.Complete();
                return new KeyValuePair<String, Om_MembershipType>("", data);
            }
        }
    }
    catch (Exception ex)
    {
        var exception = ex.Message;
        if (ex.InnerException != null)
            exception = ex.InnerException.ToString();
        return new KeyValuePair<String, Om_MembershipType>(exception, null);
    }
}

有什么方法可以在 Membership Charges collection 中获取国家实例吗？

Answer 1

Is there any way to get the Country Instance in the Membership Charges collection?

是：

var data = await membershipChargesContext
    .tblMembershipType
    .Where(i => i.MemebershipType == membershipType)
    .Include(i => i.MembershipCharges.Select(m =>  m.Country))
    .FirstOrDefaultAsync();

您可以通过后续 Select 语句扩展 Include 语句中的表达式以包含嵌套的导航属性。