Question

所以我试图仅从我的列表中获取唯一地址但由于某种原因，.Distinct无法正常工作

我试过了：

 List<Address> addresses = _db.Database.SqlQuery<Address>(
 "GetSampleAddresses @workflow_id, @records ", param1, param2).Distinct().ToList();

并且

 var json = new JavaScriptSerializer().Serialize(addresses.Distinct());

但是既没有删除重复，也不知道为什么？

Answer 1

问题在于，当您使用.Disctinct()重载而没有参数时，它将比较参考基础上的对象（通过使用默认的相等比较器）。换句话说，将两次添加到您的集合中的相同对象将被视为重复，但具有相同字段/属性的两个不同对象将不相等。
要按特定字段进行比较，您必须提供IEqualityComparer进行比较：

var json = new JavaScriptSerializer().Serialize(addresses.Distinct(new AddressComparer()));

AddressComparer本身：

class AddressComparer: IEqualityComparer<Address>
{
    public bool Equals(Address x, Address y)
    {         
        //Check whether the compared objects reference the same data. 
        if (Object.ReferenceEquals(x, y)) return true;

        //Check whether any of the compared objects is null. 
        if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
             return false;

        // Compare properties here. 
        // Assuming that two Addresses are equal when Street and Code are equal.
        return x.Street == y.Street && x.Code == y.Code;
    }    

    // If two objects are equal GetHashCode for both should return same value.
    public int GetHashCode(Address address)
    {
        if (Object.ReferenceEquals(address, null)) 
            return 0;

        int hashAddress = address.Street == null ? 0 : address.Street.GetHashCode();
        int hashCode = address.Code.GetHashCode();

        // Calculate new hash code from unique values combinaiton.
        return hashAddress ^ hashCode;
    }

}

从存储过程中获取地址对象列表的不同项

1 个答案: