Contents
- 1 Why do we prefer putting constraints in the schema rather than enforcing them at higher levels?
- 2 Why do we use constraints?
- 3 What are unique constraints and how are they enforced?
- 4 How to handle unique constraint violations [ Enterprise Guide ]?
- 5 What happens when you add a unique constraint to a table?
Why do we prefer putting constraints in the schema rather than enforcing them at higher levels?
Constraints that are best enforced in the database are usually there because they are fundamental to the structure of the data model, such as a foreign key contraint to ensure that a product has a valid category_id .
Why do we use constraints?
Constraints enforce limits to the data or type of data that can be inserted/updated/deleted from a table. The purpose of constraints is to maintain the data integrity during an update/delete/insert into a table.
What is difference between unique and primary key constraints?
PRIMARY KEY constraint differs from the UNIQUE constraint in that; you can create multiple UNIQUE constraints in a table, with the ability to define only one SQL PRIMARY KEY per each table. Another difference is that the UNIQUE constraint allows for one NULL value, but the PRIMARY KEY does not allow NULL values.
What are unique constraints and how are they enforced?
What are unique constraint violations? Unique constraints are a type of application invariants (conditions that must be held true at all times). There are two types of unique constraints: aggregate-wide and application-wide. For instance, if a customer maintains multiple addresses, you may have a requirement that each such address must be unique.
How to handle unique constraint violations [ Enterprise Guide ]?
But still, even though the data in the database will be not be corrupted, one of the requests will result in an exception that would lead to a 500 (internal server) error. Of course, the correct behavior here is to return a 400 (bad request) error, not 500.
How to handle unique constraint violations in Orm?
You do expect unique constraint violations, so you need to catch the corresponding exceptions at the lowest level possible. But where exactly? If you use an ORM, such as NHibernate or Entity Framework, then it’s going to be ISession.Dispose () (or ISession.Flush ()) and DbContext.SaveChanges () respectively.
What happens when you add a unique constraint to a table?
When a UNIQUE constraint is added to an existing column or columns in the table, by default, the Database Engine examines the existing data in the columns to make sure all values are unique. If a UNIQUE constraint is added to a column that has duplicated values, the Database Engine returns an error and does not add…