Lookup manager Name from User object in VF Page

Question

I am building a VF page for my custom object Change Request.

In my object trigger on Save, I populate the Manager field of the record with this code:

if (trigger.isBefore && (trigger.isInsert || trigger.isUpdate))
    {
          system.debug('step 3 - set Manager ID & department name');

          for (Request_for_System_Change__c r : Trigger.new) {

                  string LineManagerid = [SELECT Id, ManagerId from User where Id =: r.OwnerId].ManagerId;
                  string DeptName = [SELECT Id, Department from User where Id =: userinfo.Getuserid()].Department;
                  r.Manager__c = LineManagerId;  
                  r.Department_Name_String__c = DeptName;             
          }         
        }

an that works fine.

So now I am building a VF page I need to do something similar but in my extension class as currently it just shows the manager ID like this "Manager: 009w0000003LRsuAAZ".

So at the top of my VF page I have:

<apex:page id="ChangeRequest" StandardController="Request_for_System_Change__c" extensions="RequestForSystemChangeController"
           standardStylesheets="false" 
            showHeader="false"  >

and the field is defined like this:

<apex:pageBlockSectionItem>
    <apex:outputLabel value="Manager: "/>
        <apex:panelGrid columns="1">
            <apex:outputText value="{!get_Manager(Request_for_System_Change__c.Owner__c)}"/>
         </apex:panelGrid>
</apex:pageBlockSectionItem>

In my extension class I have this method to get the Manager from the User object:

public string get_Manager(string owner_id){
    string LineManagerid = [SELECT Id, ManagerId from User where Id =: owner_id].ManagerId;
//      string LineManagerid; // = [SELECT Id, ManagerId from User where Id =:ApexPages.currentPage().getParameters().get(‘Manager_id’)];
        string DeptName = [SELECT Id, Department from User where Id =: userinfo.Getuserid()].Department;
        return LineManagerId;  
                  //r.Department_Name_String__c = DeptName;    


}

But I am getting an error:

Unknown function get_Manager. Check spelling.

so what is the correct way to do this, and where am I going wrong?

Answer 1

<apex:outputText value="{!Manager}"/>

Few changes--

In your constructor

public class yourClassName{ 
private Request_for_System_Change__c objRequest_for_System_Change;
public  yourClassName(ApexPages.standardController stdCtrl){

objRequest_for_System_Change = (Request_for_System_Change__c)stdCtrl.getRecord();

}
public string getManager(){
    string LineManagerid = [SELECT Id, ManagerId from User where Id =: objRequest_for_System_Change.OwnerId].ManagerId;

        string DeptName = [SELECT Id, Department from User where Id =: userinfo.Getuserid()].Department;
        return LineManagerId;  
                  //r.Department_Name_String__c = DeptName;    


}
}

change get_Manager to getManager

Use standardController and assign the record to local variable for access the ownerID