Using Dynamic Apex to retrieve Picklist Values

USECASE: Fetch the picklist values from Industry field of Account sObject.

List<SelectOption> options = new List<SelectOption>();

Schema.DescribeFieldResult fieldResult = Account.Industry.getDescribe();
List<Schema.PicklistEntry> picklistEntries = fieldResult.getPicklistValues();

for (Schema.PicklistEntry picklistEntry : picklistEntries) {
    options.add(new SelectOption(picklistEntry.getLabel(), picklistEntry.getValue()));
}

return options;

OR

List<SelectOption> options = new List<SelectOption>();

Map<String, Schema.SObjectField> fieldMap = Account.getSObjectType().getDescribe().fields.getMap();
List<Schema.PicklistEntry> picklistEntries = fieldMap.get('Industry').getDescribe().getPickListValues();

for (Schema.PicklistEntry picklistEntry : picklistEntries) {
    options.add(new SelectOption(picklistEntry.getLabel(), picklistEntry.getValue()));
}

return options;

DescribeSObjectResult: Check whether the object is Custom or Standard

List<String> allCustomObjsList = new List<string>();
List<String> allStandardObjsList = new List<string>();

for(Schema.SobjectType obj : Schema.getGlobalDescribe().values()) {
    Schema.DescribeSobjectResult objResult = obj.getDescribe();
    if(objResult.isCustom()) {
        String strObjName =objResult.getname();
        allCustomObjsList.add(strObjName);
    }
    else {
        String strObjName =objResult.getname();
        allStandardObjsList.add(strObjName);
    }
}

System.debug('Custom Objects List: ' +allCustomObjsList);
System.debug('Standard Objects List: ' +allStandardObjsList);

If you need to check for a specific object, execute the below code:

Schema.DescribeSObjectResult describeAccount = Schema.sObjectType.Account;
System.debug(describeAccount.isCustom());

Similarly you can use other methods for describing sObjects, the list of which can be found below:
https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_methods_system_sobject_describe.htm

Fetch recordType Name and recordTypeId without SOQL

To avoid SOQL Limit we can use dynamic apex to get RecordTypeId. We can get a particular RecordTypeId of a particular sObject or get all recordTypeid of one sobejct in a map.

global class RecordTypeUtils {
    
    //Method to get the recordTypeId 
    public static Id recordTypeId(string obj,string recName){
        Id recTypeId;
        if(obj!= null && recName != null){
            recTypeId= Schema.getGlobalDescribe().get(obj).getDescribe().getRecordTypeInfosByName().get(recName).getRecordTypeId();
        }  
        return recTypeId;  
    }
    
    //Method to get the map of recordType Name as key and recordTypeId as value 
    public static Map<String,Id> recordTypeMap(string obj){
        Map<String,Id> recTypeNameWithIdMap=new Map<String,Id>();
        if(obj!= null){
            for(Schema.RecordTypeInfo recInfo : Schema.getGlobalDescribe().get(obj).getDescribe().getRecordTypeInfosByName().values()){
                recTypeNameWithIdMap.put(recInfo.getName(),recInfo.getRecordTypeId());
            }
        }
        return recTypeNameWithIdMap;
    } 
}

I created a record type "NewLabel" on Account object. Enter the below Apex code in Execute Anonymous window and check the output:

Map<String,Id> recTypeIdMap=RecordTypeUtils.recordTypeMap('Account');
System.debug(recTypeIdMap);
Id recId=RecordTypeUtils.recordTypeId('Account','NewLabel');
System.debug(recId);

Id recordTypeId = Schema.SObjectType.Account.getRecordTypeInfosByName().get('NewLabel').getRecordTypeId(); 
System.debug(recordTypeId);

Note that values of recId and recordTypeId in your output is same.

Check the link below to check a utility class that performs the query against the RecordType object
https://interactiveties.com/blog/2016/recordtype-utility-class.php

Apex: Get sObject details using ID

Id id = 'a0M7F000000qXgg';
Schema.sObjectType objType = id.getSObjectType();
Schema.DescribeSObjectResult objDescribe = objType.getDescribe();

System.debug(objDescribe.getName());

Similarly, you can get other sObject details using the methods described in the link below:
https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_methods_system_sobject_describe.htm

Dynamic SOQL and SOSL

To create a dynamic SOQL query at run time, use the database query method. Check the reference link for more details.

List<sObject> sobjList = Database.query(string);

To create a dynamic SOSL query at run time, use the search query method. For example:

String searchquery = 'FIND \'Edge*\' IN ALL FIELDS RETURNING Account(Id, Name), Contact, Lead';
List<List<SObject>>searchList = search.query(searchquery);

To prevent SOSL injection, use the escapeSingleQuotes method. This method adds the escape character (\) to all single quotation marks in a string that is passed in from a user. The method ensures that all single quotation marks are treated as enclosing strings, instead of database commands.

fieldList = (fieldList!=null) ? String.escapeSingleQuotes(fieldList) : fieldList;

References:
http://metillium.com/2016/03/variable-binding-in-dynamic-soql/