Check out example codes for "update multiple records with entity framework". It will help you in understanding the concepts better.

Code Example 1

using (var dbcontext = new MyModel()){
   var matchedRecords = dbcontext.DummyTable.Where(e => e.code.Equals(entry.code) && e.isValid.Equals(true)).ToList();
   matchedRecords.ForEach(e => e.isValid = false);
   dbcontext.SaveChanges();
}

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