Export Salesforce Object field names into CSV file

Sample Code

Map<String, Schema.SObjectField> fMap = Schema.getGlobalDescribe().get('Account').getDescribe().Fields.getMap();
list<string> selectFields = new list<string>();
string excelHeader = 'ApexName\n';
if (fMap != null){
    for (Schema.SObjectField ft : fMap.values()){
        Schema.DescribeFieldResult fd = ft.getDescribe();
        excelHeader += fd.getName() +'\n';
    }
}
Messaging.EmailFileAttachment csvAttc = new Messaging.EmailFileAttachment();
blob csvBlob = Blob.valueOf(excelHeader);
string csvname= 'AccountFields.csv';
csvAttc.setFileName(csvname);
csvAttc.setBody(csvBlob);
Messaging.SingleEmailMessage email =new Messaging.SingleEmailMessage();
String[] toAddresses = new list<string> {'Your Email'};
String subject = 'Account fields CSV';
email.setSubject(subject);
email.setToAddresses(toAddresses);
email.setPlainTextBody('Account Fields');
email.setFileAttachments(new Messaging.EmailFileAttachment[]{csvAttc});
Messaging.SendEmailResult [] r = Messaging.sendEmail(new Messaging.SingleEmailMessage[] {email});

Output

How to access the child records from sObject using apex in Salesforce

Sometimes we run the dynamic query based on different inputs at the time we store the data in sObject or list<sObject>
from that data sometimes we have to get the child records info, to get the child records info use the
getSobject('<relationshipName>') or getSobjects('relationshipname')

Note
 custom object relationships you would use the something similar to
sObj.getSObject('Your_Custom_Object__r')

Sample Code

sObject sObj = [SELECT Id, Name, Account.Name, Account.Owner.Name FROM Contact WHERE Id = '003B000000FgA2JIAV'];

String strContactName = (String)sObj.get('Name');
String strAccName = (String)sObj.getSobject('Account').get('Name');
String strAccOwnerName = (String)sObj.getSobject('Account').getSobject('Owner').get('Name');

System.debug('Contact Name ====> '+strContactName);
System.debug('Account Name ====> '+strAccName);
System.debug('Account Owner Name ====> '+strAccOwnerName);

Output

How to get All parent objects and child objects related to the current object

Assume Opportunity is the current object, you want to know all parent object and child objects info of the current object.

All Parent Objects

Sample Code

for(Schema.SobjectField iterator: Opportunity.SobjectType.getDescribe().fields.getMap().Values()) {
    if(iterator.getDescribe().getType() == Schema.DisplayType.REFERENCE) {
        system.debug('Parent Objects ====> '+iterator.getDescribe().getReferenceTo());
    } 
}

Output

All Child Objects

Sample Code

Schema.DescribeSObjectResult sObjectInfo = Opportunity.SObjectType.getDescribe();
for (Schema.ChildRelationship iterator: sObjectInfo.getChildRelationships()) {
  system.debug('Child Objects ====> '+iterator.getChildSObject());
}

Output

Resource
DescribeSObjectResult Class

How to check field exists or not on sobject using Apex?

Some scenarios, we need to validate field is exists or not on the object.
use below simple code it checks the field on an object if the field has existed on the object it returns true otherwise it returns false.

Example:

Boolean bHasField = Account.getSobjectType().getDescribe().fields.getMap().keySet().contains('phone');
System.debug('bHasField =====> '+bHasField);

Result: