apex:inputField can only be used with sObjects

Question

I am trying to create a custom visualforce page that saves new opportunity contact roles to an opportunity. I am having trouble creating the first step of listing out all contacts that relate to that account. The error I am getting is...

Save error: Could not resolve the entity from value binding '{!u.contact}'. can only be used with SObjects, or objects that are Visualforce field component resolvable.

I do not understand why I am receiving this error. u.contact should resolve to a Contact object, which is an sObject. Am I misunderstanding something?

Here is my code...

Controller

public class ChooseContactController 
{
    public String accountId = ApexPages.currentPage().getParameters().get('accountId');
    public Account account { get; set; }
    public List<UnfundedOpportunityContactRole> unfundedOpportunityContactRoles { get; set; }

    public ChooseContactController() 
    { 
        unfundedOpportunityContactRoles = new List<UnfundedOpportunityContactRole>();
        List<Contact> contacts = [SELECT Id, Name FROM Contact WHERE AccountId =: accountId];
        account = [SELECT Id, Name FROM Account WHERE Id =: accountId];

        for(Contact c: contacts) 
        {
            unfundedOpportunityContactRoles.add(new UnfundedOpportunityContactRole(c, 'The Man'));
        }
    }

    public void Save() {}
    public void Create() {}

    public class UnfundedOpportunityContactRole
    {
        public Contact contact { get; set; }
        public String role { get; set; }

        public UnfundedOpportunityContactRole() { }

        public UnfundedOpportunityContactRole(Contact contactParam, String roleParam)
        {
            this.contact = contactParam;
            this.role = roleParam;
        }
    }
}

VF page

<apex:page controller="ChooseContactController">
  <apex:form >
    <apex:pageBlock title="Choose a contact" mode="edit">
      <apex:pageBlockButtons >
        <apex:commandButton action="{!create}" value="New"/>
        <apex:commandButton action="{!save}" value="Save"/>
      </apex:pageBlockButtons>
        <apex:pageBlockSection title="{!account.Name}">
          <apex:dataTable value="{!unfundedOpportunityContactRoles}" var="u">
            <apex:column headerValue="Contact">
              <apex:inputField value="{!u.contact}" />
            </apex:column>
            <apex:column headerValue="Role">
              <apex:inputField value="{!u.role}" />
            </apex:column>
          </apex:dataTable>
        </apex:pageBlockSection>
    </apex:pageBlock>
  </apex:form>
</apex:page>

Answer 1

The apex:inputField value u.contact must correspond to an SObject field. That is typically done by u being a reference to an SObject and contact being an SObject field name. For your example, that SObject field would be lookup field to Contact.

apex:inputField requires meta data such as the field label that is only available from an SObject field; your class field can't provide that metadata.

Try changing your Visualforce to:

<apex:column headerValue="Contact">
    <apex:inputField value="{!u.contact.Id}" />
</apex:column>
<apex:column headerValue="Role">
    <apex:inputText value="{!u.role}" />
</apex:column>