Visualforce page: Error: Unknown property on page

Question

I'm getting -

Error: Unknown property 'Opportunity_Positioning__cStandardController.Buying_Influence__c'

Any ideas what I am doing wrong?

<apex:page standardcontroller="Opportunity_Positioning__c">
           extensions="EditableBuyingInfluenceExtension"
<apex:sectionheader title="{!$ObjectType.Buying_Influence__c.label} Edit" subtitle="{!IF(ISNULL(Buying_Influence__c.Name), 'New Buying Influence',Buying_Influence__c.Name)}"/>
    <apex:form >
        <apex:pageblock mode="edit" title="{!$ObjectType.Buying_Influence__c.label} Edit">
            <apex:pageblockbuttons >
                <apex:commandbutton value="Save" action="{!Save}"/>
                <apex:commandbutton value="Cancel" action="{!Cancel}"/>
            </apex:pageblockbuttons>
            <apex:pageblocksection title="Information" showheader="true" columns="2">
                    <apex:outputText> value="{!Opportunity_Positioning__c.Name}"/>
                    <apex:outputText> value="{!Opportunity_Positioning__c.Opportunity__c}"/>
                    <apex:pageblocksectionitem />
            <apex:pageBlockSectionItem >
                <apex:pageblocksection id="childList" columns="1" title="Buying Influence" collapsible="false">
                <apex:variable var="rowNum" value="{!ZERO}" />
                <apex:outputLabel value="No Buying Influence currently exist. Click below to Add." rendered="{!NOT(hasChildren)}"/>
                    <apex:pageBlockTable value="{!children}" var="Buying Influence" rendered="{!hasChildren}">
                    <apex:column headerValue= "Buying Influence">
                    <apex:inputfield value="{!Buying_Influence__c.Name}" required="true"/>
                    <apex:column headerValue= "SCOP">
                    <apex:inputfield value="{!Buying_Influence__c.SCOP__c}" required="true"/>
                    <apex:column headerValue= "Influencer Name">
                    <apex:inputfield value="{!Buying_Influence__c.Influencer_Name__c}" required="true"/>
                    <apex:column headerValue= "Buying Influence role">
                    <apex:inputfield value="{!Buying_Influence__c.Buying_influence_role__c}" required="true"/>
                    <apex:column headerValue= "Degree of Influence">
                    <apex:inputfield value="{!Buying_Influence__c.Degree_of_Influence__c}" required="true"/>
                    <apex:pageblocksectionitem />
               </apex:column>
               <apex:pageblocksection title="How well is based covered for this contact" showheader="true" columns="2">
               </apex:pageblocksection>
               </apex:column> headerValue="Rating for base covered">
                    <apex:inputfield value="{!Buying_Influence__c.Rating_for_base_covered__c}" required="true"/>
               </apex:column> headerValue="Equivalent Collinson Stakeholder">
                    <apex:inputfield value="{!Buying_Influence__c.Equivalent_Collinson_Stakeholder__c}" required="false"/>
               </apex:column> headerValue="Evidence to support your rating">
                    <apex:inputfield value="{!Buying_Influence__c.Evidence_to_support_your_rating__c}" required="false"/>
                    </apex:column>
                    <apex:column headerValue=" ">
                    <!-- This is the second half of the trick to keep track
                    of your row index for deletion. -->
                    <apex:variable var="rowNum" value="{!rowNum + 1}" />
                    <apex:commandLink value="Delete" action="{!removeFromList}" rerender="childList,messages" immediate="true"> 
     <apex:param name="removeIndex" assignTo="{!removeIndex}" value="{!rowNum}" />
            </apex:commandLink>
          </apex:column>
        </apex:pageBlockTable>
        <apex:commandButton value="Add Buying Influence" action="{!addToList}" rerender="childList, messages" immediate="true" />
      </apex:pageBlockSection>
     </apex:pageblocksectionitem>
     </apex:outputtext> </apex:outputtext>
    </apex:pageblocksection>
</apex:pageblock>
</apex:form>
</apex:page>

Answer 1

You are trying to use "Buying_Influence__c" object directly, while the standardcontoller refers to "Opportunity_Positioning__c".

Create an apex controller refer it using extension and access the "Buying_Influence__c" object via that controller.

Answer 2

Your standard controller is Opportunity_Positioning__c. You can refer to those fields directly, but in your controller extension, you must still do a query for the Buying_Influence__c record you're trying to show fields on.

If Buying_Influence__c is a parent object to Opportunity_Positioning, then just put Opportunity_Positioning__c before every Buying_Influence__c reference.