Define maximum length for strings

Define maximum length for strings

When creating a SQL database via code first it is important to tell EF Core how long a string can be otherwise it will always be translated to NVARCHAR(MAX). This has performance implications as well as other problems like not being able to create an index on that column. Also a rogue application could flood the database.

Having this model:

public class BlogPost
{
  public int Id { get; private set; }
  public string Title { get; private set; }
  public string Content { get; private set; }
}

❌ Bad Not defining the maximum length of a string will lead to NVARCHAR(max).

public class BlogPostConfiguration : IEntityTypeConfiguration<BlogPost>
{
    public void Configure(EntityTypeBuilder<BlogPost> builder)
    {
        builder.HasKey(c => c.Id);
        builder.Property(c => c.Id).ValueGeneratedOnAdd();
    }
}

Will lead to generation of this SQL table:

CREATE TABLE BlogPosts
(
  [Id] [int] NOT NULL,
  [Title] [NVARCHAR](MAX) NULL,
  [Content] [NVARCHAR](MAX) NULL
)

✅ Good Defining the maximum length will reflect also in the database table.

public class BlogPostConfiguration : IEntityTypeConfiguration<BlogPost>
{
    public void Configure(EntityTypeBuilder<BlogPost> builder)
    {
        builder.HasKey(c => c.Id);
        builder.Property(c => c.Id).ValueGeneratedOnAdd();

        // Set title max length explicitly to 256
        builder.Property(c => c.Title).HasMaxLength(256);
    }
}

Will lead to generation of this SQL table:

CREATE TABLE BlogPosts
(
  [Id] [int] NOT NULL,
  [Title] [NVARCHAR](256) NULL, -- Now it only can hold 256 characters
  [Content] [NVARCHAR](MAX) NULL
)