✨ 70 sentinel values (#78)

* Added SentinelValues.csproj

* Added sentinel values

EfCoreSamples.sln

@@ -66,6 +66,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "EnhancedBulkUpdateAndDelete
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "HierarchyIds", "HierarchyIds\HierarchyIds.csproj", "{B18EB327-BF8D-4D61-B9F1-8392A9678F55}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SentinelValues", "SentinelValues\SentinelValues.csproj", "{EFE525A3-2D62-4A00-B354-12E1D0BE247D}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -188,6 +190,10 @@ Global
 		{B18EB327-BF8D-4D61-B9F1-8392A9678F55}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{B18EB327-BF8D-4D61-B9F1-8392A9678F55}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{B18EB327-BF8D-4D61-B9F1-8392A9678F55}.Release|Any CPU.Build.0 = Release|Any CPU
+		{EFE525A3-2D62-4A00-B354-12E1D0BE247D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{EFE525A3-2D62-4A00-B354-12E1D0BE247D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{EFE525A3-2D62-4A00-B354-12E1D0BE247D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{EFE525A3-2D62-4A00-B354-12E1D0BE247D}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

SentinelValues/Account.cs

@@ -0,0 +1,22 @@
+namespace SentinelValues;
+
+public class Account
+{
+    public int Id { get; private set; }
+
+    // One way to use sentinel values is to use a nullable backing field
+    private int? _balance;
+    public int Balance
+    {
+        get => _balance ?? 100;
+        set => _balance = value;
+    }
+
+    // Another way to use sentinel values is to use a sentinel value that's been configured in ApplicationDbContext
+    public int Credits { get; set; } = -1;
+
+    public override string ToString()
+    {
+        return $"Id: {Id}, Balance: {Balance}, Credits: {Credits}";
+    }
+}

SentinelValues/ApplicationDbContext.cs

@@ -0,0 +1,20 @@
+using Common;
+using Microsoft.EntityFrameworkCore;
+
+namespace SentinelValues;
+
+public class ApplicationDbContext : DbContext
+{
+    public DbSet<Account> Accounts => Set<Account>();
+
+    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
+    {
+        optionsBuilder
+            .UseSqlServer(DbConnectionFactory.Create("SentinelValues"));
+    }
+
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        modelBuilder.Entity<Account>().Property(a => a.Credits).HasDefaultValue(10).HasSentinel(-1);
+    }
+}

SentinelValues/Program.cs

@@ -0,0 +1,24 @@
+using Microsoft.EntityFrameworkCore;
+using SentinelValues;
+
+Console.WriteLine("Sentinel Values Sample");
+
+using var db = new ApplicationDbContext();
+db.Database.EnsureDeleted();
+db.Database.EnsureCreated();
+
+var accounts = new List<Account>
+{
+    new(),
+    new() { Balance = 0, Credits = 0 }, // NOTE: Without Sentinel values this would use the defaults of Balance=100, and Credits=10.
+    new() { Balance = 100, Credits = 10 },
+};
+
+db.Accounts.AddRange(accounts);
+db.SaveChanges();
+
+var allAccounts = db.Accounts.ToList();
+Console.WriteLine("All Account");
+allAccounts.ForEach(Console.WriteLine);
+
+Console.ReadLine();

SentinelValues/SentinelValues.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net8.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+</Project>

SentinelValues/readme.md

@@ -0,0 +1,15 @@
+# Sentinel Values and Database Defaults
+
+EF Core can configure SQL Server to use Database defaults.  For this to work, EF needs to know when NOT to send a value to the DB so that the DB can use the default value.  It does this by using the `default` value of the .NET CLR type  This works well for reference types, but not value types.
+
+However, in some cases the CLR default value is a value valid to insert.  For example, a default makes sense when creating a record.  But what if you want to create a record with the default CLR value?  Previously you couldn't.  This is where Sentinel Values come in.
+
+## Use Cases
+
+- Inserting rows with default CLR values when the DB has a default value
+- Correct EF Core behavior when using boolean `default` and `enum` default values
+- Overriding defaults for other value types such as `int`, `DateTime`,  etc.
+
+## Resources
+
+- [EF Core Docs | Sentinel Values and Database Defaults](https://learn.microsoft.com/en-us/ef/core/what-is-new/ef-core-8.0/whatsnew#database-defaults-for-enums)