Update lookup field programmatically in sharepoint 2010 using COM

Question

I created a Lookup list component using javascript and HTML to view the values of the lookup list in sharepoint 2010. and it works great for viewing.

is it possible to update the lookup field programmatically using COM (Client Object Model)?

to read the lookup, I use this code:

currList.get_item("LOOKUP_FIELD_NAME")[i].get_lookupValue();

how can i set lookup value?

Answer 1

I found the solution:

ctx = new SP.ClientContext.get_current();

//Add code to retrieve current list item...

var newId = 11;//for exmple

var newLookupField = new SP.FieldLookupValue();
newLookupField.set_lookupId(newID);
var existingLookupValue = currList.get_item("Lookup_field_id");

if (existingLookupValue == null) {
    // set to a single lookup value because we don’t have an existing value
    currList.set_item("Lookup_field_id", newLookupField);

} else if ( existingLookupValue instanceof SP.FieldLookupValue) {
    // we need to change from a lookup field value to an array of lookup fields values
    var newLookupValue = new Array();
    newLookupValue[0] = existingLookupValue;
    newLookupValue[1] = newLookupField;
    currList.set_item("Lookup_field_id", newLookupValue);
} else if ( existingLookupValue instanceof Array) {
    // array already exists, just append
    existingLookupValue[existingLookupValue.length] = newLookupField;
    currList.set_item("Lookup_field_id", existingLookupValue);
}

currentItem.update();

ctx.executeQueryAsync(Function.createDelegate(this, this.onUpdateLookupSucceeded), Function.createDelegate(this, this.onUpdateLookupFailed));

finally, to set the lookup field empty, you can simply set its value to null

currList.set_item("Lookup_field_id", null);

HTH, Khalil.