How to use LINQ to query from a list of objects into an existing object?

I'm not sure if this is possible in LINQ, but I have the following scenario:

I'm calling a SharePoint list service multiple times with multiple queries. I am then populating a single object and its properties from all of the queries. I am using LINQ to query the XElement returned. I know that if the call gets to this point, that there will only ever be one item returned from my LINQ query. I currently have to query into a new object and then set the properties of my main object from this new object (from LINQ), for each web service call. (The below code sample contains only a small portion of the 'Action' item properties that would need to b开发者_如何转开发e queried and set.)

Is there any way to make the below statement 'select' into my existing 'action' object?

var item = (from listItem in result.GetSPListItems()
            select new ContractAction
            {
                Title = listItem.GetSPFieldValue("Title"),
                Description = listItem.GetSPFieldValue("Description"),
                DeliveryOrderID = SPHelper.GetFirstLookupID(listItem.GetSPFieldValue("Delivery Order")),
                EstimatedValue = ((listItem.GetSPFieldValue("Estimated Value") as double?) ?? 0),
                AgreementTypeID = SPHelper.GetFirstLookupID(listItem.GetSPFieldValue("Contract Type")),                                                
            }).FirstOrDefault();

contractAction.Title = item.Title;
contractAction.Description = item.Description;
contractAction.DeliveryOrderID = item.DeliveryOrderID;
contractAction.EstimatedValue = item.EstimatedValue;
contractAction.AgreementTypeID = item.AgreementTypeID;

---

Can't you simply:

action = (from listItem in result.GetSPListItems()
         select new Action
         {
             Title = listItem.GetSPFieldValue("Title"),
             Description = listItem.GetSPFieldValue("Description"),
             DeliveryOrderID = SPHelper.GetFirstLookupID(listItem
                 .GetSPFieldValue("Delivery Order")),
             EstimatedValue = 
                 ((listItem.GetSPFieldValue("Estimated Value") as double?) ?? 0),
             AgreementTypeID = SPHelper.GetFirstLookupID(listItem
                 .GetSPFieldValue("Contract Type")),
         }).FirstOrDefault();

---

Firstly you should rename the class Action because Action is a defined delegate in the built-in library. I'll use MyAction in the following code.

And if you always need to get MyAction from SPListItem, you'd better write a extension method to put the logic in one place for DRY(Don't Repeat Yourself).

public static MyAction ToMyAction(this SPListItem item)
{
    return new MyAction  
       {  
          Title = item.GetSPFieldValue("Title"),  
          Description = item.GetSPFieldValue("Description"),  
          DeliveryOrderID = SPHelper.GetFirstLookupID(item.GetSPFieldValue("Delivery Order")),  
          EstimatedValue = ((item.GetSPFieldValue("Estimated Value") as double?) ?? 0),  
          AgreementTypeID = SPHelper.GetFirstLookupID(item.GetSPFieldValue("Contract Type"))                                                  
       };  
}

var action = result.GetSPListItems()
                   .Select(item => item.ToMyAction())
                   .FirstOrDefault();
//var action = (from item in result.GetSPListItems()
//              select item.ToMyAction()).FirstOrDefault();

---

First, since I know I'm only going to have one result I just had to be willing to remove the idea of using the 'select' part of a linq query. Once I did that, the answer was obvious.

//just grab the first item
var item = result.GetSPListItems().FirstOrDefault();

//then grab the properties into the existing ContractActionEntity                             
contractAction.Title = item.GetSPFieldValue("Title");
contractAction.Description = item.GetSPFieldValue("Description");
contractAction.DeliveryOrderID = SPHelper.GetFirstLookupID(item.GetSPFieldValue("Delivery Order"));
contractAction.EstimatedValue = item.GetSPFieldValue("Estimated Value").ToNullableDouble();
contractAction.AgreementTypeID = SPHelper.GetFirstLookupID(item.GetSPFieldValue("Contract Type")),

Thanks everyone for making me think more about the problem and leading me in the direction of the answer.

---

You could write your queries in one big query. So for example you could have:

var item = (from listItem in result.GetSPListItems()
        from query2Outer in result.SecondQuery().Where(x => x.ItemEdp == it.ItemEdp).DefaultIfEmpty() // This is an outer join
        select new Action
        {
            //if the one query didn't return an item then it sets the properties to the default values
            Example = (query2Outer == null ? "Default Value" : query2Outer.Example),
            Title = listItem.GetSPFieldValue("Title"),
            Description = listItem.GetSPFieldValue("Description"),
            DeliveryOrderID = SPHelper.GetFirstLookupID(listItem.GetSPFieldValue("Delivery Order")),
            EstimatedValue = ((listItem.GetSPFieldValue("Estimated Value") as double?) ?? 0),
            AgreementTypeID = SPHelper.GetFirstLookupID(listItem.GetSPFieldValue("Contract Type")),                                                
        }).FirstOrDefault();

---

An alternative to the extension methods approach would be:

public static void SelectFirstInto(this IEnumerable<ContractAction> items, ContractAction target)
{
    var source = items.FirstOrDefault();

    if(source != null)
    {
        target.Title = source.Title,  
        target.Description = source.Description ,  
        target.DeliveryOrderID = source.DeliveryOrderID,  
        target.EstimatedValue = source.EstimatedValue, 
        target.AgreementTypeID = source.AgreementTypeID                                                 
     }
}

Then you could do:

ContractAction targetAction = new ContractAction();
var item = (from listItem in result.GetSPListItems()
            select new ContractAction
            {
                Title = listItem.GetSPFieldValue("Title"),
                Description = listItem.GetSPFieldValue("Description"),
                DeliveryOrderID = SPHelper.GetFirstLookupID(listItem.GetSPFieldValue("Delivery Order")),
                EstimatedValue = ((listItem.GetSPFieldValue("Estimated Value") as double?) ?? 0),
                AgreementTypeID = SPHelper.GetFirstLookupID(listItem.GetSPFieldValue("Contract Type")),                                                
            }).SelectFirstInto(targetAction);

Keep in mind that if the list is empty, then the target object remains unmodified. This may be something you'll want to handle accordingly.