Can Lists Be Stored Efficiently in a Relational Database Column?

Storing a List in a Database Column: Can It Be Done?

When faced with the task of storing complex objects like lists within a relational database, the question arises: can this be accomplished while adhering to database normalization principles?

In the provided example, the object of interest, FOO, contains a list of fruits. The requirement is to persist this list in a database column. However, traditional relational database schemas discourage storing unstructured data like lists within a single column.

The Relational Database Approach

The solution lies in a denormalized design known as a junction table. In this approach, we create a separate table, FOOFruits, that stores the relationship between the FOO objects and the fruits they contain. Each row in this table represents a link between a specific FOO object and a fruit.

To define the table structure:

CREATE TABLE FOO (
  id int primary key not null,
  int1 int,
  int2 int,
  int3 int
);

CREATE TABLE Fruits (
  id int primary key not null,
  name varchar(30)
);

CREATE TABLE FOOFruits (
  FruitID int references Fruits (ID),
  FooID int references FOO(id),
  constraint pk_FooFruits primary key (FruitID, FooID)
);

By using this approach, we ensure data integrity and avoid inconsistencies while maintaining the referential integrity of the FOO and Fruits tables.

For instance, to add the fruit "Apple" to the FOO object with ID=5:

INSERT FOOFruits(FooID, FruitID)
SELECT 5, ID FROM Fruits WHERE name = 'Apple';

This method allows for efficient querying and retrieval of the fruit lists associated with each FOO object.

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