お世話になっております。

２つの選択リスト仮にAとBとします。

このAとB、２つの選択リストどちらかを選択しないとエラーになり
さらに両方選択してあった場合にもエラーを出すにはどのような入力規則で
制御するのが良いのでしょうか。

ご指導お願いします。
 

public class getBFromA {
    public ObjectA__c obj_a;
    public List <ObjectB__c> obj_bs { get; set; }
    public getBFromA(ApexPages.StandardController controller) {
        this.obj_a = (ObjectA__c)controller.getRecord();
    }
    
    public List<ObjectB__c> getBonlyA(){
        obj_bs = new List <ObjectB__c> ();
        obj_bs = [SELECT Id,
                            Name
                        FROM ObjectB__c
                        WHERE ObjectBtoA__c = :obj_a.Id
                    ];
        System.debug('ObjectB' + obj_bs);
        return obj_bs;
    }
}

<apex:page standardController="ObjectA" extensions="getBFromA" title="getBFromA">
    <apex:form >
        <apex:pageBlock title="getBFromA" id="getBFromA">
            <apex:pageBlockTable value="{!obj_bs}" var="b">
                <apex:column value="{!b.Id}"/>
                <apex:column value="{!b.Name}"/>
            </apex:pageBlockTable>
        </apex:pageBlock>
    </apex:form>
</apex:page>

15:11:03:017 VARIABLE_ASSIGNMENT [5]|this.obj_a|{"s":1,"v":{"CurrencyIsoCode":"JPY","Id":"*******obj_aのid******","Name":"ObjectAの名前"}}|0x4f25b83e

<apex:commandButton action="{!doSearch}" value="検索" />

return new PageReference('/' + オブジェクト.Id);

[
  {
    "message": "The REST API is not enabled for this Organization.",
    "errorCode": "API_DISABLED_FOR_ORG"
  }
]

alert('ID::'+'{!Cobj__c.ID}');
alert('ID__c::'+'{!Cobj__c.ID__c}');

if({!$User.ProfileId}== "00e10000000lQ9F")
{
	alert("このユーザはこのボタンを使用することができません。");
} else{
　//ボタンの動作
}

I have a simple joined soql query i'm using
SELECT Id, FirstName, LastName, Email, (SELECT AccountId, CreatedDate, ActivityDate, Subject, Description, ActivityType, CallType from ActivityHistories) FROM Contact WHERE Id = '".$id."'"

which works great for me. Now I want to get info from a custom object called 'Position__c', so i've added it to the selects
SELECT Id, FirstName, LastName, Email, (SELECT AccountId, CreatedDate, ActivityDate, Subject, Description, ActivityType, CallType from ActivityHistories), (SELECT Id, Position_title__c, End_Date__c FROM Position__c) FROM Contact WHERE Id = '".$id."'"

But I get an error with that, quoting 'Didn't understand relationship 'Position__c' in FROM part of query call.' I have also tried it with 'Position__r' also but get the same error.

Can anyone help me to run a successful query?

お世話になっております。

２つの選択リスト仮にAとBとします。

このAとB、２つの選択リストどちらかを選択しないとエラーになり
さらに両方選択してあった場合にもエラーを出すにはどのような入力規則で
制御するのが良いのでしょうか。

ご指導お願いします。
 

public class getBFromA {
    public ObjectA__c obj_a;
    public List <ObjectB__c> obj_bs { get; set; }
    public getBFromA(ApexPages.StandardController controller) {
        this.obj_a = (ObjectA__c)controller.getRecord();
    }
    
    public List<ObjectB__c> getBonlyA(){
        obj_bs = new List <ObjectB__c> ();
        obj_bs = [SELECT Id,
                            Name
                        FROM ObjectB__c
                        WHERE ObjectBtoA__c = :obj_a.Id
                    ];
        System.debug('ObjectB' + obj_bs);
        return obj_bs;
    }
}

<apex:page standardController="ObjectA" extensions="getBFromA" title="getBFromA">
    <apex:form >
        <apex:pageBlock title="getBFromA" id="getBFromA">
            <apex:pageBlockTable value="{!obj_bs}" var="b">
                <apex:column value="{!b.Id}"/>
                <apex:column value="{!b.Name}"/>
            </apex:pageBlockTable>
        </apex:pageBlock>
    </apex:form>
</apex:page>

15:11:03:017 VARIABLE_ASSIGNMENT [5]|this.obj_a|{"s":1,"v":{"CurrencyIsoCode":"JPY","Id":"*******obj_aのid******","Name":"ObjectAの名前"}}|0x4f25b83e