Update list object based on other LINQ / LAMBDA

Here are my two objects

    public class ObjectHeaderBuffer
    {
       public int DataObjectId { get; set; }
       public string FileName { get; set; }
       public int RowCount { get; set; }
       public string Checksum 开发者_C百科{ get; set; }
       public int ReconTarget { get; set; }
    } 

    public class ObjectHeaderAttribute
    {
       public int DataObjectId { get; set; }
       public int AttributeType { get; set; }
       public int AttributeValue { get; set; }

    }

        var ohBuffer = new List<ObjectHeaderBuffer>();
        var ohAttribute = new List<ObjectHeaderAttribute>();

I want to update ohBuffer.ReconTarget with ohAttribute.AttributeValue where ohBuffer.DataObjectId == ohAttribute.DataObjectId

what is linq or lambda of this?

---

You need to iterate each item in ohBuffer and look up the value in ohAttribute.

Assuming there is only one Attribute for each Buffer, this will work.

ohBuffer.ForEach(b => b.ReconTarget = ohAttribute
    .SingleOrDefault(a => a.DataObjectId == b.DataObjectId).AttributeValue);

---

If the lookup returns null, you can either coalesce to a new object and take the default value

ohBuffer.ForEach(b => b.ReconTarget = 
    (ohAttribute.SingleOrDefault(a => a.DataObjectId == b.DataObjectId) 
         ?? new ObjectHeaderAttribute())
        .AttributeValue);

or you could just take null

ohBuffer.ForEach(b => b.ReconTarget = 
    {
        var attribute = ohAttribute
            .SingleOrDefault(a => a.DataObjectId == b.DataObjectId);

        if (attribute == null)
            return null;
        return attribute.AttributeValue;
    });

---

They way i did is:

 foreach (var objectHeaderBuffer in ohBuffer)
        {
            var objectHeaderAttribute = (from c in ohAttribute where c.DataObjectId == objectHeaderBuffer.DataObjectId select c).First();
            objectHeaderBuffer.ReconTarget = objectHeaderAttribute.AttributeValue;
        }

---

If your relation is 1:1 Then

 foreach (ObjectHeaderBuffer Itemx in ohBuffer)
 {
    ObjectHeaderAttribute Itemy= (from ObjectHeaderAttribute c in ohAttribute where c.DataObjectId == Itemx.DataObjectId select c).FirstOrDefault();
    if(Itemy!=null)
    {
        Itemx .ReconTarget = Itemy.AttributeValue;
    }
  }

Or

foreach (ObjectHeaderBuffer Itemx in ohBuffer)
{
        ObjectHeaderAttribute Itemy= ohAttribute.Where(c=>c.DataObjectId == Itemx .DataObjectId).FirstOrDefault();
        if(Itemy!=null)
        {
            Itemx .ReconTarget = Itemy.AttributeValue;
        }
}