How to retrieve lookup values using ClientContext?

Question

What's the best way to retrieve lookup values using ClientContext? I'm accessing a list using ClientContext (let's call it ParentList). That list contains several lookup fields (let's call one of them ChildId) pointing to other lists (call one of them ChildList). I'm currently using a ListItem to iterate over the results. Snippet:

ListItemCollection collListItem = oList.GetItems(camlQuery);

context.Load(collListItem,
    items => items.Include(
    item => item["title"],
    item => item["id"]));

context.ExecuteQuery();

foreach (ListItem oListItem in collListItem)
{           
    allTrials.Add(new Trial
    {
        Name = oListItem["title"].ToString(),
        Category = oListItem["id"].ToString(),
    });

}

I don't have anything regarding the lookup values in it yet because I haven't been able to wrap my head around that. I'm assuming I'll need to use "FieldLookupValue", but haven't used that before.

Thx!

Answer 1

Retrieving a lookup field is no different than retrieving any other field, but getting at the value takes an extra step.

(using your example)

var childIdField = oListItem["ChildId"] as FieldLookupValue;

if (childIdField != null)
{
    var childId_Value = childIdField.LookupValue;
    var childId_Id = childIdField.LookupId;
}

The reason for the extra step is the field stores the value as both the Id and the Value, and if you use the .ToString() method on the field, it will return a string of the Id and Value with a ";#" seperator (if I remember correctly, I don't have it in front of me so the exact seperating string may be slightly different).

If the field is a multi-value lookup field, the result is an array of FieldLookupValues and the result will need to be cast and iteratted over to get individual values.

var childIdField = oListItem["ChildId"] as FieldLookupValue[];

if (childIdField != null)
{
    foreach(var lookupValue in childIdField)
    {
        var childId_Value = lookupValue.LookupValue;
        var childId_Id = lookupValue.LookupId;
    }
}

All code should be considered psuedo-code as I wrote it in the reply box. I wouldn't expect it to cut/paste and compile without being looked over for proper syntax -- but it should illustrate the steps needed to use lookup field values.

Answer 2

the class SP.FieldLookupValue has two properties:

• lookupid

• lookupvalue

You can use the following sample code:

...
var itemsEnumerator = collListItem.getEnumerator();
while(itemsEnumerator.moveNext()){

    var currentItem = itemsEnumerator.get_current();
    var myId = currentItem.get_item('FIELD').get_lookupId();
    var myTitle = currentItem.get_item('FIELD').get_lookupValue();

    var result = 
        {
             Id: myId,
             Title: myTitle
         };
 };
...