How to assign to all class data members at once

问题

In a Dapper ORM application, I want to assign one object to another, or all data members at once. Like this:

public class TableA
{
    public int    UserId   { get; set; }
    public string ClientId { get; set; }
    // ... more fields ...

    public bool Query()
    {
        bool Ok = false;
        try{
            // Method A
            TableA Rec = QueryResultRecords.First(); 
            MyCopyRec(Rec, this);                        // ugly

            // Method B
            this = QueryResultRecords.First();           // avoids CopyRec, does not work

            Ok = true;
        }
        catch(Exception e){
            Ok = false;
        }
        return Ok;
    }
}

With Method A you can assign the object from .First() directly to a new object of class TableA, and need a custom method MyCopyRec to get the data in the data members of the same class.

However, with Method B you cannot assign the same object directly to this.

Or is there another way to do this?

回答1:

You cannot assign a object to "this" if "this" is a reference type, e.g. a class. "this" is a pointer to the current class instance. This would only work if this is a value type, e.g. a struct.

You can only assign values to properties of "this" (which is what probably happens in the (CopyRec method), like:

var result = QueryResultRecords.First();
this.UserId  = result.UserId;

回答2:

/// <summary>
/// Extension for 'Object' that copies the properties to a destination object.
/// </summary>
/// <param name="source">The source.</param>
/// <param name="destination">The destination.</param>
public static void CopyProperties(this object source, object destination)
{
    // If any this null throw an exception
    if (source == null || destination == null)
        throw new ArgumentException("Source or/and Destination Objects are null");
    // Getting the Types of the objects
    Type typeDest = destination.GetType();
    Type typeSrc = source.GetType();

    // Iterate the Properties of the source instance and  
    // populate them from their desination counterparts  
    PropertyInfo[] srcProps = typeSrc.GetProperties();
    foreach (PropertyInfo srcProp in srcProps)
    {
        if (!srcProp.CanRead)
        {
            continue;
        }
        PropertyInfo targetProperty = typeDest.GetProperty(srcProp.Name);
        if (targetProperty == null)
        {
            continue;
        }
        if (!targetProperty.CanWrite)
        {
            continue;
        }
        if ((targetProperty.GetSetMethod().Attributes & MethodAttributes.Static) != 0)
        {
            continue;
        }
        if (!targetProperty.PropertyType.IsAssignableFrom(srcProp.PropertyType))
        {
            continue;
        }
        // Passed all tests, lets set the value
        targetProperty.SetValue(destination, srcProp.GetValue(source, null), null);
    }
}

Here's that method I talked about in the comments above.

Also refer to this link: Apply properties values from one object to another of the same type automatically?

来源：https://stackoverflow.com/questions/33392575/how-to-assign-to-all-class-data-members-at-once

标签

object