EF Core SQL Server Sparse Columns

In SQL Server, a sparse column is a column that is optimized for storing null values. Sparse columns allow you to save storage space by not storing any data for columns that have a null value.

When you create a sparse column, you need to specify the SPARSE attribute. For example, the following SQL statement creates a table with a sparse column:

CREATE TABLE Books (
   Price INT SPARSE,
   Name VARCHAR(50)
);

In this example, the Price is a sparse column, while the Name is a regular column. When a row is inserted into the Books table and the Price value is null, SQL Server will not allocate any space to store the null value.

Sparse columns can be useful in situations where you have a large number of columns in a table, and many of those columns have null values. By using sparse columns, you can reduce the amount of storage space needed for the table, which can improve performance and reduce storage costs.

Support for Sparse Columns in EF Core

When working with a SQL Server database that contains sparse columns, EF Core will create corresponding entity properties that are nullable. For example, if you have a table named Products with a sparse column named Price, and a non-sparse column named Name, the EF Core code to represent this table might look something like this:

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal? Price { get; set; }
}

The Price property is nullable (decimal?) to account for the fact that the sparse column may contain null values. When EF Core retrieves data from the database, it will populate the Price property with null if the corresponding database value is null.

To configure a sparse column in EF Core, you can use the IsSparse in OnModelCreating.

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder
        .Entity<Product>()
        .Property(e => e.Price)
        .IsSparse();
}

The IsSparse method allows you to specify that a Price column should be treated as a sparse column in the database.

CREATE TABLE [dbo].[Products] (
    [Id]    INT                    IDENTITY (1, 1) NOT NULL,
    [Name]  NVARCHAR (MAX)         NOT NULL,
    [Price] DECIMAL (18, 2) SPARSE NULL,
    CONSTRAINT [PK_Products] PRIMARY KEY CLUSTERED ([Id] ASC)
);

Limitations

EF Core supports working with SQL Server sparse columns by representing them as nullable entity properties. However, there are some limitations and provider-specific considerations to be aware of.

• EF Core does not support creating unique indexes on sparse columns, and you cannot include sparse columns in a clustered index.
• Additionally, not all database providers support sparse columns - for example, the SQLite provider does not support them.