First Commit

Author: [email protected]

.gitignore

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+obj/
+bin/
+.idea/

LazyLoader.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "LazyLoader", "LazyLoader\LazyLoader.csproj", "{A49EF347-A6B4-4B78-A97B-DCAFE706BB90}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{A49EF347-A6B4-4B78-A97B-DCAFE706BB90}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A49EF347-A6B4-4B78-A97B-DCAFE706BB90}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A49EF347-A6B4-4B78-A97B-DCAFE706BB90}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A49EF347-A6B4-4B78-A97B-DCAFE706BB90}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+EndGlobal

LazyLoader/.gitignore

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+bin/
+obj/
+.idea/

LazyLoader/Context.cs

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+using System;
+using Microsoft.EntityFrameworkCore;
+
+#nullable disable
+
+namespace LazyLoader
+{
+    public partial class Context : DbContext
+    {
+        public Context()
+        {
+        }
+
+        public Context(DbContextOptions<Context> options)
+            : base(options)
+        {
+        }
+
+        public virtual DbSet<Email> Emails { get; set; }
+        public virtual DbSet<ParticipantList> ParticipantLists { get; set; }
+
+        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
+        {
+            if (!optionsBuilder.IsConfigured)
+            {
+#warning To protect potentially sensitive information in your connection string, you should move it out of source code. You can avoid scaffolding the connection string by using the Name= syntax to read it from configuration - see https://go.microsoft.com/fwlink/?linkid=2131148. For more guidance on storing connection strings, see http://go.microsoft.com/fwlink/?LinkId=723263.
+                optionsBuilder
+                    .UseLazyLoadingProxies()
+                    .LogTo(Console.WriteLine)
+                    .EnableSensitiveDataLogging(true);
+                
+                base.OnConfiguring(optionsBuilder);
+            }
+        }
+
+        protected override void OnModelCreating(ModelBuilder modelBuilder)
+        {
+            modelBuilder.Entity<Email>(entity =>
+            {
+                entity.HasOne(d => d.ParticipantList)
+                    .WithMany(p => p.Emails)
+                    .HasForeignKey(d => d.ParticipantListId)
+                    .OnDelete(DeleteBehavior.ClientSetNull);
+            });
+            OnModelCreatingPartial(modelBuilder);
+        }
+
+        partial void OnModelCreatingPartial(ModelBuilder modelBuilder);
+    }
+}

LazyLoader/Email.cs

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+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Microsoft.EntityFrameworkCore;
+
+#nullable disable
+
+namespace LazyLoader
+{
+    [Table("emails")]
+    public partial class Email
+    {
+        [Key]
+        [Column("id", TypeName = "integer")]
+        public long Id { get; set; }
+        [Column("participant_list_id", TypeName = "integer")]
+        public long? ParticipantListId { get; set; }
+        [Required]
+        [Column("email_address")]
+        public string EmailAddress { get; set; }
+
+        [Required]
+        [ForeignKey(nameof(ParticipantListId))]
+        [InverseProperty("Emails")]
+        public virtual ParticipantList ParticipantList { get; set; }
+    }
+}

LazyLoader/LazyLoader.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net5.0</TargetFramework>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <PackageReference Include="Microsoft.EntityFrameworkCore" Version="6.0.0-preview.4.21253.1" />
+      <PackageReference Include="Microsoft.EntityFrameworkCore.Proxies" Version="6.0.0-preview.4.21253.1" />
+      <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="6.0.0-preview.4.21253.1" />
+    </ItemGroup>
+
+</Project>

LazyLoader/ParticipantList.cs

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+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Microsoft.EntityFrameworkCore;
+
+#nullable disable
+
+namespace LazyLoader
+{
+    [Table("participant_lists")]
+    [Index(nameof(Name), IsUnique = true)]
+    public partial class ParticipantList
+    {
+        public ParticipantList()
+        {
+            Emails = new HashSet<Email>();
+        }
+
+        [Key]
+        [Column("id")]
+        public long Id { get; set; }
+        [Column("name")]
+        public string Name { get; set; }
+
+        [InverseProperty(nameof(Email.ParticipantList))]
+        public virtual ICollection<Email> Emails { get ; set; }
+    }
+}

LazyLoader/Program.cs

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+using System;
+using System.IO;
+using System.Linq;
+using Microsoft.EntityFrameworkCore;
+
+namespace LazyLoader
+{
+    class Program
+    {
+        private static readonly string dataFilename = "LazyLoader.db";
+
+        static private void DumpEntities(ParticipantList plist)
+        {
+            Console.WriteLine($"-------\nParticipantList '{plist.Name}' Id={plist.Id}");
+            foreach (var email in plist.Emails)
+            {
+                Console.WriteLine($"\t{email.Id}: {email.EmailAddress}");
+            }
+            Console.WriteLine("-------\n");
+        }
+        
+        static void Main(string[] args)
+        {
+            Console.WriteLine("Why doesn't lazy loading work?");
+
+            System.IO.File.Delete(dataFilename);
+            var options = new DbContextOptionsBuilder<Context>()
+                .UseSqlite($"Data Source={dataFilename};")
+                .Options;
+            var db = new Context(options);
+            db.Database.EnsureCreated();
+
+            var plist = new ParticipantList()
+            {
+                Name = "I'm a P List"
+            };
+            var email1 = new Email()
+            {
+                EmailAddress = "[email protected]",
+                ParticipantList = plist,
+            };
+            var email2 = new Email()
+            {
+                EmailAddress = "[email protected]",
+                ParticipantList = plist,
+            };
+            db.ParticipantLists.Add(plist);
+            db.Emails.Add(email1);
+            db.Emails.Add(email2);
+            db.SaveChanges();
+
+            Console.WriteLine($"Before Clearing LazyLoadingEnabled={db.ChangeTracker.LazyLoadingEnabled}:");
+            DumpEntities(plist);
+
+            Console.WriteLine($"Clearing Change Tracker");
+            Console.WriteLine($"via LazyLoading LazyLoadingEnabled={db.ChangeTracker.LazyLoadingEnabled}");
+            db.ChangeTracker.Clear();
+            var persisted_plist = db.ParticipantLists.Find(plist.Id);
+            DumpEntities(persisted_plist);
+
+            var emails = db.Emails.Where(u => u.ParticipantListId == plist.Id);
+            Console.WriteLine($"After Also selecting emails from DB LazyLoadingEnabled={db.ChangeTracker.LazyLoadingEnabled}");
+            DumpEntities(persisted_plist);
+
+            Console.WriteLine($"Clearing Change Tracker");
+            Console.WriteLine($"via Include LazyLoadingEnabled={db.ChangeTracker.LazyLoadingEnabled}");
+            db.ChangeTracker.Clear();
+            persisted_plist = db.ParticipantLists.Where(u => u.Id == plist.Id).Include(pl => pl.Emails).First();
+            DumpEntities(persisted_plist);
+
+        }
+    }
+}