检查数据库中是否已存在列表项的最佳方法是什么？

Question

I have a list of a person object that i want to insert in the database, but first i need to know if every person of the list already exists in the database or not. (I'm not using any ORM like EntityFramework, just ADO.NET of Oracle provider)

For example:

var listOfPersons = new List<Person>(); //this list could have 100 of person objects
     
//I need to check if every person of a list already exists in the database
foreach(var person in listOfPersons)
{
   //Here we made the call to the database for every person.
   //We make the query in the database to a table that could have millions of records        
   var existInDb = db.ExistPersonInDb(person.DocumentId); 

   //If not exists insert in the database
}

I need to know if this approach is the best way or not, because in this example i'll open/close the connection for every person in the list and then go to query the database to a table that could have a millions of records.

Or i could call the database just once and bring the millions of records of the table and assign it to a list.

Like this:

var personsInDb = db.getPersonsInDb().ToList(); //Get all the persons from database and add it to a list

var listOfPersons = new List<Person>(); //this list could have 100 of person objects

//I need to check if every person of a list already exists in the database
 foreach(var person in listOfPersons)
 {  
    //And here with Linq just check if the person that i want to insert already exists in the personsInDb list     
    var existInDb = personsInDb.Exists(p => p.DocumentId== person.DocumentId); 

    //If not exists insert in the database
 }

Of this two example what is the best way to solve this problem that i have? Or if you have another solution please let me know.

Answer 1

You can check for existence of records in a single call ( similar like where id in () . And get all those id or some unique key for which no entry present in the table. And then insert rows into the table. You can do bulk insert also.

Answer 2

var listOfPersons = new List<Person>();
var inputPersonIds = listOfPersons.Select(p => p.Id).ToList();

Modify db.getPersonsInDb() method to pass the inputPersonIds using the in keyword while preparing the sql command.

For eg:

select * from person where id in inputPersonIds