schema

Sobject : Any one the objects created in the salesforce to store the data using declarative format is called subject

Ex: Account ,Customer__c, Lead,Contact

Account  a; //a is instance of sobject Account

Contact con;// con is instance of subject Contact

IF we want to know instace belongs to which object  we can use method getSobjectType();

Public Sobject getSobjectType() : This method will specify instace of subject belongs to which subject.

Ex:

Account  a=new Account() ;

System.debug(a.getSobjectType()) ;// Account

Contact c=new Contact();

System.debug(c.getSobjectType()) ; //contact

Account.SobjectType will specify that it is an instance of subject Account.

            Account.SobjectType  a;

            System.debug(a.getSobjectType()) ;// Account;

Class :Schema.SobjectType ;

Schema .SobjectType : This will specify the subject type we are referring to

1.getDescribe() : This method will return the description about subject on which we have called

Synatax : public  Schema.DescribeSobjectResult  getDescribe()

Ex :      Schema.DescribeSobjectResult result=Account.SobjectType.getDescribe();

2.newSobject() : This will construt new subject of the type we have specified

            Public  Sobject newSobject()

Ex:  Account a=Account.SobjectType.newSobject();

            Sobject s=Contact.SobjectType.newSobject();

3.newSobjectId(Id)

This method is used to create new subject with referring to the existing  record  ( just like clone of record)

When you write a soql query we are  getting the reference to the existing records

 Ex: Account  a=[select id ,name ,Inudstry from Account where name=’sam’ limit 1];

            a.name,a.industry

          Simillarly we can create a reference of subject using the schema;

            Account a=new Account(Name=’aaa’);

            Insert a;

Account acc=Account.SobjectType(a.id); / /this will  create a new Account object similar to

                                                                                    Subject a ;

4.newSobject(Id,Boolean) :

This will create a new subject with given recordType and default values

Public Sobject newSobject(id recordTypeId, Boolean default)

getGlobalDescribe() : This  method is defined in the schema namespace which is used to fetch the all the subjects with their corresponding name  in the form of map

Syntax :public Map<String,Schema.SobjectType>  getGlobalDescribe()

Map<String,Schema.SobjectType> mymap ;

Where key is string  which is the name of the subject.

Value is Schema.SobjectType which will store the sobject Type

Map<String,Schema.SobjectType>  objMap=schema.getGlobalDescribe();

Fetch all the objects names from Map

Set<String> objectNames=objMap.keySet();

Q: How to get the description about the subject.

Ex 1:

Schema.SobjectType s=Account.sobjectType;

Schema.DescribeSobjectResult result=s.getDescribe();

Ex 2:

Schema.DescribeSobjectResult result=Contact.SobjectType.getDescribe();

Scneario : Create a picklist field in the vf page with list of all the subjects in your org and  when you select the subject corresponding description of the object should be displayed

Apex Class :

public class SchemaExample {

    public Map<String,Schema.SObjectType> objMap {set;get;}

    public List<SelectOption> options {set;get;}

    public String selected {set;get;}

    public String result {Set;get;}

    public SchemaExample(){

        objMap=Schema.getGlobalDescribe();

        Set<String> keys=objMap.keySet();

        options=new List<SelectOption>();

        for(String s:keys){

            SelectOption op=new SelectOption(s,s);

            options.add(op); 

        }

    }

    public  void getDesc(){

         Schema.SobjectType s=objMap.get(selected);

        Schema.DescribeSobjectResult res=s.getDescribe();

        result=''+res;

    }

}

VF page:

<apex:page controller="SchemaExample">

            <apex:form>

                        <apex:selectList value="{!selected}" size="1">

                <apex:selectOptions value="{!options}" />

                <apex:actionSupport  event="onchange" action="{!getDesc}" reRender="one"/>

            </apex:selectList>

            <apex:outputLabel value="{!result}" id="one"/>

            </apex:form>

</apex:page>

How to fetch list of fields from the object

1.Get the description of the subject

Schema.DescribeSobjectResult  result=Account.SobjectType.getDescribe();

Map<String,Schema.SobjectField>  fldMap=result.fields.getMap();

This map contains key as field name and Value as field

Scenario : Create a piclist which will display list of customobjects as picklist option when we select any one of the object it has to display list of corresponding fields in the object .

public class SchemaExampl2 {

    public Map<String,Schema.SObjectType> objMap{set;get;}

    public Map<String,Schema.SObjectField> fldMap{Set;get;}

    public List<selectOption> objoptions{set;get;}

    public List<SelectOption> fldoptions{set;get;}

    public String selected {set;get;}

    public SchemaExampl2(){

        objMap=schema.getGlobalDescribe();

        Set<String> keys=objMap.keySet();

        objoptions=new List<selectOption>();

        fldoptions=new List<Selectoption>();

        fldoptions=new List<selectOption>();

        selectOption s1=new SelectOption('none','-none-');

        fldoptions.add(s1);

        for(string s:keys){

            Schema.DescribeSobjectResult res=objMap.get(s).getDescribe();

            if(res.isCustom()){

                        SelectOption op=new SelectOption(s,s);

                        objoptions.add(op);

            }

        } 

    }

    public void getDesc(){

         Schema.DescribeSobjectResult res=objMap.get(selected).getDescribe();

         fldMap=res.fields.getMap();

        for(String s:fldMap.keySet()){

            SelectOption op=new SelectOption(s,s);

            fldoptions.add(op);

        }

    }

}

<apex:page controller="SchemaExampl2" >

    <apex:form>

            <apex:pageBlock title="Schema">

            <apex:pageBlockSection title="SchemaExample">

                        <apex:selectList value="{!selected}" size="1">

                    <apex:selectOptions value="{!objOptions}" />

                    <apex:actionSupport event="onchange" action="{!getDesc}" reRender="one"/>

                </apex:selectList>

                <apex:selectList size="1" id="one">

                    <apex:selectOptions value="{!fldoptions}" />

                </apex:selectList>

            </apex:pageBlockSection>

        </apex:pageBlock>

    </apex:form>

</apex:page>

How to create a new picklist field referring to the selected picklist field from theobject.

Class :

public class SchemaExample3 {

    public List<SelectOption> options {set;get;}

    public String fldType{Set;get;}

    public SchemaExample3(){

            options=new List<selectOption>();

            Schema.DescribeFieldResult result=Account.Industry.getDescribe();

            fldType=''+result.getType();

            List<Schema.PicklistEntry> opt=result.getPicklistValues();

            for(Schema.PicklistEntry p:opt){

                        SelectOption op=new SelectOption(p.getValue(),p.getLabel());

                options.add(op);

            }

         

       

    }

}

<apex:page controller="SchemaExample3" >

    <apex:form>{!fldType}

            <apex:selectList size="1">

            <apex:selectOptions value="{!options}" />

        </apex:selectList>

    </apex:form>

</apex:page>