Custom form template with external list does not work

Question

I have following .ascx file

<%@ Assembly Name="Microsoft.Web.CommandUI, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
<%@ Register TagPrefix="SharePoint" Namespace="Microsoft.SharePoint.WebControls" Assembly="Microsoft.SharePoint, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
<%@ Register TagPrefix="Utilities" Namespace="Microsoft.SharePoint.Utilities" Assembly="Microsoft.SharePoint, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
<%@ Register TagPrefix="asp" Namespace="System.Web.UI" Assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" %>
<%@ Register TagPrefix="WebPartPages" Namespace="Microsoft.SharePoint.WebPartPages" Assembly="Microsoft.SharePoint, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
<%@ Import Namespace="Microsoft.SharePoint" %>
<%@ Control Language="C#" AutoEventWireup="false" %>
<SharePoint:RenderingTemplate runat="server" ID="CustomListForm">
  <Template>
    <asp:Label runat="server" Text="This is the CustomListForm template." />
  </Template>
</SharePoint:RenderingTemplate>

The custom template is used when displaying an item in the following internal list instance

<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
  <ListInstance Title="InternalListInstance"
                OnQuickLaunch="TRUE"
                TemplateType="100"
                FeatureId="00bfea71-de22-43b2-a848-c05709900100"
                Url="Lists/InternalListInstance"
                CustomSchema="InternalListInstance\Schema.xml"
                Description="Internal List">
  </ListInstance>
</Elements>

with schema defined as

<?xml version="1.0" encoding="utf-8" ?>
<List Title="InternalListInstance" Direction="none" Url="Lists/InternalListInstance" BaseType="0" Type="100" FolderCreation="FALSE" DisableAttachments="TRUE" xmlns:ows="Microsoft SharePoint" xmlns="http://schemas.microsoft.com/sharepoint/">
  <MetaData>
    <ContentTypes>
      <ContentType ID="0x01" Name="Item" Group="List Content Types" Description="Create a new list item." FeatureId="{695b6570-a48b-4a8e-8ea5-26ea7fc1d162}">
        <Folder TargetName="Item" />
        <FieldRefs>
          <FieldRef ID="{c042a256-787d-4a6f-8a8a-cf6ab767f12d}" Name="ContentType" />
          <FieldRef ID="{fa564e0f-0c70-4ab9-b863-0177e6ddd247}" Name="Title" Required="TRUE" ShowInNewForm="TRUE" ShowInEditForm="TRUE" />
        </FieldRefs>
        <XmlDocuments>
          <XmlDocument NamespaceURI="http://schemas.microsoft.com/sharepoint/v3/contenttype/forms">
            <FormTemplates xmlns="http://schemas.microsoft.com/sharepoint/v3/contenttype/forms">
              <Display>CustomListForm</Display>
              <Edit>ListForm</Edit>
              <New>ListForm</New>
            </FormTemplates>
          </XmlDocument>
        </XmlDocuments>
      </ContentType>
    </ContentTypes>
    <Fields>
    </Fields>
    <Forms>
      <Form Type="DisplayForm" Url="DispForm.aspx" SetupPath="pages\form.aspx" Template="CustomListForm" WebPartZoneID="Main" />
      <Form Type="EditForm" Url="EditForm.aspx" SetupPath="pages\form.aspx" Template="ListForm" WebPartZoneID="Main" />
      <Form Type="NewForm" Url="NewForm.aspx" SetupPath="pages\form.aspx" Template="ListForm" WebPartZoneID="Main" />
    </Forms>
    <Views>
      <View BaseViewID="1" Type="HTML" WebPartZoneID="Main" DisplayName="All Items" DefaultView="TRUE" MobileView="TRUE" MobileDefaultView="TRUE" SetupPath="pages\viewpage.aspx" ImageUrl="/_layouts/images/generic.png" Url="AllItems.aspx">
        <Toolbar Type="Standard" />
        <XslLink>main.xsl</XslLink>
        <RowLimit Paged="TRUE">30</RowLimit>
        <ViewFields>
          <FieldRef Name="Attachments"></FieldRef>
          <FieldRef Name="LinkTitle"></FieldRef>
        </ViewFields>
        <Query>
          <OrderBy>
            <FieldRef Name="ID"></FieldRef>
          </OrderBy>
        </Query>
      </View>
    </Views>
  </MetaData>
</List>

The custom form template is not used when displaying an item in the following external list instance

<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
  <ListInstance Title="ExternalListInstance"
                OnQuickLaunch="TRUE"
                TemplateType="600"
                Url="Lists/ExternalListInstance"
                CustomSchema="ExternalListInstance\Schema.xml"
                Description="External List">
    <DataSource>
      <Property Name="LobSystemInstance" Value="MyLobSystem" />
      <Property Name="EntityNamespace" Value="MyNamespace" />
      <Property Name="Entity" Value="Coworker" />
      <Property Name="SpecificFinder" Value="ReadItem" />
    </DataSource>
  </ListInstance>
</Elements>

with schema defined as

<?xml version="1.0" encoding="utf-8" ?>
<List Title="ExternalListInstance" Direction="none" Url="Lists/ExternalListInstance" BaseType="0" Type="600" FolderCreation="FALSE" DisableAttachments="TRUE" xmlns:ows="Microsoft SharePoint" xmlns="http://schemas.microsoft.com/sharepoint/">
  <MetaData>
    <ContentTypes>
      <ContentType ID="0x01" Name="Item" Group="List Content Types" Description="Create a new list item." FeatureId="{695b6570-a48b-4a8e-8ea5-26ea7fc1d162}">
        <Folder TargetName="Item" />
        <FieldRefs>
          <FieldRef ID="{c042a256-787d-4a6f-8a8a-cf6ab767f12d}" Name="ContentType" />
          <FieldRef ID="{fa564e0f-0c70-4ab9-b863-0177e6ddd247}" Name="Title" Required="TRUE" ShowInNewForm="TRUE" ShowInEditForm="TRUE" />
        </FieldRefs>
        <XmlDocuments>
          <XmlDocument NamespaceURI="http://schemas.microsoft.com/sharepoint/v3/contenttype/forms">
            <FormTemplates xmlns="http://schemas.microsoft.com/sharepoint/v3/contenttype/forms">
              <Display>CustomListForm</Display>
              <Edit>ListForm</Edit>
              <New>ListForm</New>
            </FormTemplates>
          </XmlDocument>
        </XmlDocuments>
      </ContentType>
    </ContentTypes>
    <Fields>
      <Field DisplayName="BDC Identity" Hidden="FALSE" Name="BdcIdentity" SourceID="http://schemas.microsoft.com/sharepoint/v3" StaticName="BdcIdentity" Type="Text" />
      <Field DisplayName="Coworker ID" Hidden="FALSE" Name="CoworkerId" SourceID="http://schemas.microsoft.com/sharepoint/v3" StaticName="CoworkerId" Type="Integer" />
      <Field DisplayName="First Name" Hidden="FALSE" Name="FirstName" SourceID="http://schemas.microsoft.com/sharepoint/v3" StaticName="FirstName" Type="Text" />
      <Field DisplayName="Last Name" Hidden="FALSE" Name="LastName" SourceID="http://schemas.microsoft.com/sharepoint/v3" StaticName="LastName" Type="Text" />
      <Field DisplayName="Email" Hidden="FALSE" Name="Email" SourceID="http://schemas.microsoft.com/sharepoint/v3" StaticName="Email" Type="Text" />
      <Field DisplayName="Account" Hidden="FALSE" Name="SamAccountName" SourceID="http://schemas.microsoft.com/sharepoint/v3" StaticName="SamAccountName" Type="Text" />
      <Field DisplayName="Personnel Number" Hidden="FALSE" Name="PersonnelNumber" SourceID="http://schemas.microsoft.com/sharepoint/v3" StaticName="PersonnelNumber" Type="Text" />
      <Field DisplayName="Birthday" Hidden="FALSE" Name="Birthday" SourceID="http://schemas.microsoft.com/sharepoint/v3" StaticName="Birthday" Type="DateTime" />
    </Fields>
    <Forms>
      <Form Type="DisplayForm" Url="DispForm.aspx" SetupPath="pages\form.aspx" Template="CustomListForm" WebPartZoneID="Main" />
      <Form Type="EditForm" Url="EditForm.aspx" SetupPath="pages\form.aspx" Template="ListForm" WebPartZoneID="Main" />
      <Form Type="NewForm" Url="NewForm.aspx" SetupPath="pages\form.aspx" Template="ListForm" WebPartZoneID="Main" />
    </Forms>
    <Views>
      <View BaseViewID="1" Type="HTML" WebPartZoneID="Main" DisplayName="Read List" DefaultView="TRUE" MobileView="TRUE" MobileDefaultView="TRUE" SetupPath="pages\viewpage.aspx" ImageUrl="/_layouts/images/generic.png" Url="ReadList.aspx">
        <Toolbar Type="Standard" />
        <Method Name="ReadList" />
        <XslLink>main.xsl</XslLink>
        <RowLimit Paged="TRUE">30</RowLimit>
        <ViewFields>
          <FieldRef Name="CoworkerId" />
          <FieldRef Name="FirstName" />
          <FieldRef Name="LastName" />
          <FieldRef Name="Email" />
          <FieldRef Name="SamAccountName" />
        </ViewFields>
        <Query>
          <OrderBy>
            <FieldRef Name="CoworkerId"></FieldRef>
          </OrderBy>
        </Query>
      </View>
    </Views>
  </MetaData>
</List>

At no time SharePoint 2010 accepts the declarations for the custom form templates. The form template $l.Forms[0].TemplateName and the content type form template $l.ContentTypes[0].DisplayFormTemplateName is set to ListForm. Trying to change the content type's template throws following error

$l.ContentTypes[0].DisplayFormTemplateName = "CustomListForm"
$l.ContentTypes[0].Update()
Exception calling "Update" with "0" argument(s): "The collection cannot be modified."
At line:1 char:26
+ $l.ContentTypes[0].Update <<<< ()
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : DotNetMethodException

I have the feeling that custom form templates do not work with external lists. Am I right?

Answer 1

In your Schema.xml, you're assosciating the CustomListForm with the Item content type, not your BCS entity.

I think what you want to do here is, inside the <Forms> tag for the List Definition, insert the link to your custom form and put UseLegacyForms to true.