There is a restriction on number of characters (255 characters) allowed for a Multi line text field added to a document library when you try to input more than 255 characters through UI.
Attaching a sample code which will help in working around the problem of restriction on number of characters (255 characters) allowed for a Multi line text field added to a document library.
SPSite mySite = new SPSite(“
SPWeb myWeb = mySite.OpenWeb();
WE SHOULD USE USING HERE I AM NOT ?
SPList myList = myWeb.Lists[“
SPField myField = myList.Fields[“MULTILINE-FIELDNAME”];
((SPFieldMultiLineText)myField).UnlimitedLengthInDocumentLibrary = true;
and you can also make the same things with site column definition in element.xml
The Multiple Lines of Text Field
The Lookup Field
The Lookup field is the only field type that cannot be created with a simple feature such as this one. The cause for this is the fact that this type of field references a column of a list using the list’s ID, and a list’s ID is dynamically generated when a list is created.
This means that there is no way one can predict what will be the ID of the list referenced by the Lookup field when the feature is developed. This value is only known when the feature is activated in a specific web site.
But we can write feature receiver for that and can write code on feature activation