如何在C＃中遍历通用对象属性

Question

The problem is that I often encounter a scene that needs to traverse the instance object's property as another object method incoming parameters when the method calls. Like follows:

//Step 1
var criteria =new Criteria();
SqlCommand cmd =SqlCommandManager.GetDataCommand("SearchOrderList");
//Step 2
//The define of the SetParameterValue method is :
//public void SetParameterValue(string paramName, object val);
cmd.SetParameterValue("@SellerID",criteria.SellerID );
cmd.SetParameterValue("@DateFrom", criteria.SentDateFrom);
cmd.SetParameterValue("@DateTo", criteria.SentDateTo);
cmd.SetParameterValue("@StartRowIndex", criteria.PagingInfo.StartRowIndex);
cmd.SetParameterValue("@PageSize", criteria.PagingInfo.PageSize);
cmd.SetParameterValue("@SortField", criteria.PagingInfo.SortField);
cmd.SetParameterValue("@SortType", criteria.PagingInfo.SortType);
//cmd.SetPa........
//Step 3
cmd.ExecuteEntityList<Model>();

How I make a flexible and scalable method to simplify step 2. I have a thought is that make a Generic Method to deal this:

public static void SetParameterValues<T>(this DataCommand cmd,T _object)
    {
        if (Object.ReferenceEquals(cmd,null))
            throw new ArgumentException("The Parameter cmd must be not null", "cmd");
        if (!object.ReferenceEquals(_object, null))
        {
            //to do ...
        }

    }

but I'm confused what I should Proceed to deal with next step(I have made an extension Method). So could you guys help me check out this problem?

Answer 1

Instead of making one method generic and then have do somehow differentiate between the different types, create overloaded versions of the method

public static void SetParameterValue(this DataCommand cmd, string parameter, int value)
public static void SetParameterValue(this DataCommand cmd, string parameter, string value)
public static void SetParameterValue(this DataCommand cmd, string parameter, DateTime value)
...

Eg

public static void SetParameterValue(this DataCommand cmd, string parameter, int value)
{
    if (Object.ReferenceEquals(cmd,null))
        throw new ArgumentException("The Parameter cmd must be not null", "cmd");
    cmd.Parameters.Add(parameter, SqlDbType.Int).Value = value;
}

But if you want to infer the prameter name, you would have to use another approach. To be able to access the property name, you need an expression tree:

public static void SetParameterValue<T>(this DataCommand cmd, Expression<Func<T>> expr)
{
    var member = expr.Body as MemberExpression;
    if (member == null)
        throw new ArgumentException("We need a member expression of type obj.PropertyName");

    var prop = member.Member as PropertyInfo;
    if (prop == null)
        throw new ArgumentException("We need a property, not a field");

    string name = prop.Name;
    T value = expr.Compile()();

    cmd.Parameters.AddWithValue("@" + name, value);
}

You must then call it using a lambda expression

cmd.SetParameterValue(() => criteria.SellerID);