Trigger to check duplicates in salesforce using "from date" and "to date"

 

Here is the Sample code to prevent update and insert records between from date and end date in salesforce. This trigger have two events:-
before insert and before update

trigger Duplicatecheck on <Obejct> (before insert,before update) {
    set<object > ListOfrecords= new set<object >([SELECT id,Valid_Form__c,Valid_To__c FROM <object>]);
    for(<object>  obj1 : ListOfrecords) {
        for(<object> obj2: Trigger.new) {
            if(obj2.VS_State__c== obj1.VS_State__c && obj2.vs_Tax_Type__c == obj1 .vs_Tax_Type__c){
                if((obj2.Valid_To__c >= obj1.Valid_Form__c&& obj2.Valid_To__c <= obj1 .Valid_To__c ) ||
                   (obj2.Valid_Form__c>= obj1.Valid_Form__c&& obj2.Valid_To__c <= obj1 .Valid_To__c ) ||
                   (obj2.Valid_Form__c>= obj1.Valid_Form__c&& obj2.Valid_Form__c<= obj1 .Valid_To__c ) ||
                   (obj2.Valid_Form__c< obj1.Valid_To__c && obj2.Valid_To__c > obj1 .Valid_To__c )){
                       obj2.addError('record already exist between these dates.');
                   }
            }
        }
    }
}
Output:-

Trigger to prevent insert or update duplicate records.