change attributes of a site column when using in list definition

Question

i want to know how to change Required Property on site column when it is consumed in a list definition.

like i have deployed a site column

<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
 <Field ID ="{aae098f7-c7b0-4236-a8ec-9908e9acf2a0}" 
         Name="ABC" 
         Type="Lookup" 
         UnlimitedLengthInDocumentLibrary="TRUE" 
         DisplayName=" " 
         List="Lists/Directory" 
         ShowField="Title" 
         Required="FALSE"
         Group="Custom"
         Overwrite="TRUE"
         OverwriteInChildScopes="TRUE"
         Description=""
         />
</Elements>

i have declared it Required="FALSE" for a list Definition but when i reuse this column in another list definition i want to set it Mandatory, so in the content type that i have defined in the list definition (schema.xml) i made it Required="TRUE" as:

 <ContentTypes>
      <ContentType ID="0x01001CC809EB1E174539A92FDA8EEA9CABFD"
                   Name="xyz"
                   Group="custom CT"
                   Description=""
                   Inherits="FALSE"
                   Version="0">
        <FieldRefs>
          <FieldRef ID ="{97BA70AA-BC2C-496C-8565-56F99ABF91A4}" Name="R"/>
          <FieldRef ID="{61389c59-cf0e-45ab-a6b4-30dca223f47c}" Name="C"/>
          <FieldRef ID="{aae098f7-c7b0-4236-a8ec-9908e9acf2a0}" Name="ABC"/>
        </FieldRefs>
      </ContentType>
    </ContentTypes>
    <Fields>
      <Field ID ="{97BA70AA-BC2C-496C-8565-56F99ABF91A4}" Name="R" Type="Lookup" DisplayName="$Resources:Region" List="Lists/Regions" ShowField="Title" Required="TRUE" />
      <Field ID="{61389c59-cf0e-45ab-a6b4-30dca223f47c}" Name="C" Type="Lookup" DisplayName="$Resources:Country"   List="Lists/Countries" ShowField="Title" Required="TRUE"></Field>
      <Field ID ="{aae098f7-c7b0-4236-a8ec-9908e9acf2a0}" Name="ABC" Type="Lookup" DisplayName="$Resources:ABC" List="Lists/Brands" ShowField="Title" Required="TRUE" />
    </Fields>

but it will remain not required . is there any way to make it required for one list , and not required for other list .

thankx in advance

Answer 1

What you are doing (changing the XML schema of a field or content type while it is in use) is unsupported. ANY changes to fields done AFTER deployment and usage should be done using code (or in SP2010 using FeatureUpgradeActions! This is because the schema is saved (ghosted) to the content database.

Furthermore, it is not possible to have the same schema behave differently for 2 lists (i.e. field required in list A and not required in list B). A Content type is list agnostic, meaning it knows nothing about the list using it. The content type is actually "copied" to the list (notice the extra GUID in the ctype id when editing from list settings?). Any changes in behavior per list means creating either separate content types, or changing the field behavior for the content type in the list (settings) itself.

Answer 2

What you want to do is possible. Try setting Required in the Content Type:

  <ContentType ID="0x01001CC809EB1E174539A92FDA8EEA9CABFD"
               Name="xyz"
               Group="custom CT"
               Description=""
               Inherits="FALSE"
               Version="0">
    <FieldRefs>
      <FieldRef ID ="{97BA70AA-BC2C-496C-8565-56F99ABF91A4}" Name="R" Required="TRUE"/>
      <FieldRef ID="{61389c59-cf0e-45ab-a6b4-30dca223f47c}" Name="C" Required="TRUE"/>
      <FieldRef ID="{aae098f7-c7b0-4236-a8ec-9908e9acf2a0}" Name="ABC" Required="TRUE"/>
    </FieldRefs>
  </ContentType>