Better optionals

benchmarks/NexusMods.MnemonicDB.Benchmarks/Benchmarks/ReadThenWriteBenchmarks.cs

@@ -61,7 +61,7 @@ public async Task<ulong> ReadThenWrite()
         using var tx = Connection.BeginTransaction();
         var mod = Mod.Load(Connection.Db, _modId);
         var oldHash = mod.OptionalHash;
-        tx.Add(_modId, Mod.OptionalHash, Hash.From(oldHash.Value + 1));
+        tx.Add(_modId, Mod.OptionalHash, Hash.From((ulong)oldHash.Value + 1));
         var nextdb = await tx.Commit();
 
         var loadout = Loadout.Load(Connection.Db, mod.LoadoutId);

src/NexusMods.MnemonicDB.Abstractions/Attributes/ScalarAttribute.cs

@@ -1,6 +1,8 @@
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using DynamicData.Kernel;
 using JetBrains.Annotations;
+using NexusMods.MnemonicDB.Abstractions.IndexSegments;
 using NexusMods.MnemonicDB.Abstractions.Models;
 
 namespace NexusMods.MnemonicDB.Abstractions.Attributes;
@@ -32,84 +34,77 @@ public bool Contains<T>(T entity) where T : IHasIdAndIndexSegment
     }
 
     /// <summary>
-    ///   Gets the value of the attribute from the entity.
+    ///  Tries to get the value of the attribute from the entity.
     /// </summary>
-    public TValue Get(IHasIdAndIndexSegment entity)
+    public bool TryGetValue<T>(T entity, IndexSegment segment, [NotNullWhen(true)] out TValue? value)
+        where T : IHasEntityIdAndDb
     {
-        var segment = entity.IndexSegment;
-        var dbId = entity.Db.AttributeCache.GetAttributeId(Id);
-        for (var i = 0; i < segment.Count; i++)
+        var attributeId = entity.Db.AttributeCache.GetAttributeId(Id);
+        foreach (var datom in segment)
         {
-            var datom = segment[i];
-            if (datom.A != dbId) continue;
-            return ReadValue(datom.ValueSpan, datom.Prefix.ValueTag, entity.Db.Connection.AttributeResolver);
+            if (datom.A != attributeId) continue;
+            value = ReadValue(datom.ValueSpan, datom.Prefix.ValueTag, entity.Db.Connection.AttributeResolver);
+            return true;
         }
 
-        if (DefaultValue.HasValue)
-            return DefaultValue.Value;
-
-        ThrowKeyNotfoundException(entity);
-        return default!;
+        value = default!;
+        return false;
     }
-    
+
     /// <summary>
-    ///   Gets the value of the attribute from the entity, this performs a lookup in the database
-    /// so prefer using the overload with IHasIdAndIndexSegment if you already have the segment.
+    /// Tries to get the value of the attribute from the entity.
     /// </summary>
-    protected TValue Get(IHasEntityIdAndDb entity)
+    public bool TryGetValue<T>(T entity, [NotNullWhen(true)] out TValue? value)
+        where T : IHasIdAndIndexSegment
     {
-        var segment = entity.Db.Get(entity.Id);
-        var dbId = entity.Db.AttributeCache.GetAttributeId(Id);
-        for (var i = 0; i < segment.Count; i++)
-        {
-            var datom = segment[i];
-            if (datom.A != dbId) continue;
-            return ReadValue(datom.ValueSpan, datom.Prefix.ValueTag, entity.Db.Connection.AttributeResolver);
-        }
-
-        if (DefaultValue.HasValue)
-            return DefaultValue.Value;
-
-        ThrowKeyNotfoundException(entity);
-        return default!;
+        return TryGetValue(entity, segment: entity.IndexSegment, out value);
     }
 
     /// <summary>
-    /// Retracts the attribute from the entity.
+    /// Gets the value of the attribute from the entity.
     /// </summary>
-    public void Retract(IAttachedEntity entityWithTx)
+    public TValue Get<T>(T entity, IndexSegment segment)
+        where T : IHasEntityIdAndDb
     {
-        Retract(entityWithTx, Get(entityWithTx));
+        if (TryGetValue(entity, segment, out var value)) return value;
+        return ThrowKeyNotfoundException(entity.Id);
     }
 
-    private void ThrowKeyNotfoundException(IHasEntityIdAndDb entity)
+    /// <summary>
+    /// Gets the value of the attribute from the entity.
+    /// </summary>
+    public TValue Get<T>(T entity)
+        where T : IHasIdAndIndexSegment
     {
-        throw new KeyNotFoundException($"Entity {entity.Id} does not have attribute {Id}");
+        var segment = entity.IndexSegment;
+        return Get(entity, segment);
     }
 
     /// <summary>
-    ///   Try to get the value of the attribute from the entity.
+    /// Gets the value of the attribute from the entity, <see cref="DefaultValue"/>, or <see cref="Optional{TValue}.None"/>.
     /// </summary>
-    public bool TryGet(IHasIdAndIndexSegment entity, out TValue value)
+    public Optional<TValue> GetOptional<T>(T entity)
+        where T : IHasIdAndIndexSegment
     {
-        var segment = entity.IndexSegment;
-        var dbId = entity.Db.AttributeCache.GetAttributeId(Id);
-        for (var i = 0; i < segment.Count; i++)
-        {
-            var datom = segment[i];
-            if (datom.A != dbId) continue;
-            value = ReadValue(datom.ValueSpan, datom.Prefix.ValueTag, entity.Db.Connection.AttributeResolver);
-            return true;
-        }
+        if (TryGetValue(entity, entity.IndexSegment, out var value)) return value;
+        return DefaultValue.HasValue ? DefaultValue : Optional<TValue>.None;
+    }
 
-        if (DefaultValue.HasValue)
-        {
-            value = DefaultValue.Value;
-            return true;
-        }
+    /// <summary>
+    /// Retracts the attribute from the entity.
+    /// </summary>
+    public void Retract(IAttachedEntity entityWithTx)
+    {
+        Retract(entityWithTx, value: Get(entityWithTx, segment: entityWithTx.Db.Get(entityWithTx.Id)));
+    }
 
-        value = default!;
-        return false;
+    [DoesNotReturn]
+    private TValue ThrowKeyNotfoundException(EntityId entityId)
+    {
+        throw new KeyNotFoundException($"Entity `{entityId}` doesn't have attribute {Id}");
+#pragma warning disable CS0162 // Unreachable code detected
+        return default!;
+#pragma warning restore CS0162 // Unreachable code detected
     }
 
     /// <summary>

src/NexusMods.MnemonicDB.SourceGenerator/Template.weave

@@ -416,8 +416,12 @@ public partial class {{= model.Name}} : __MODELS__.IModelFactory<{{= model.Name}
            {{elif attr.IsReference}}
            public {{= attr.ReferenceType.ToDisplayString()}}Id {{= attr.ContextualName}} => {{= attr.ReferenceType.ToDisplayString()}}Id.From({{= attr.FieldName}}.Get(this));
            {{else}}
+           {{if attr.IsOptional}}
+           public global::DynamicData.Kernel.Optional<{{= attr.HighLevelType.ToDisplayString()}}> {{= attr.ContextualName }} => {{= attr.FieldName}}.GetOptional(this);
+           {{else}}
            public {{= attr.HighLevelType.ToDisplayString()}} {{= attr.ContextualName}} => {{= attr.FieldName}}.Get(this);
            {{/if}}
+           {{/if}}
 
 
            {{if attr.IsReference && attr.IsScalar}}

tests/NexusMods.MnemonicDB.Tests/DbTests.cs

@@ -541,13 +541,13 @@ public async Task CanReadAndWriteOptionalAttributes()
 
         var remapped = result.Remap(modWithDescription);
         remapped.Contains(Mod.Description).Should().BeTrue();
-        Mod.Description.TryGet(remapped, out var foundDesc).Should().BeTrue();
+        Mod.Description.TryGetValue(remapped, remapped.IndexSegment, out var foundDesc).Should().BeTrue();
         foundDesc.Should().Be("Test Description");
-        remapped.Description.Should().Be("Test Description");
-        
+        remapped.Description.Value.Should().Be("Test Description");
+
         var remapped2 = result.Remap(modWithoutDiscription);
         remapped2.Contains(Mod.Description).Should().BeFalse();
-        Mod.Description.TryGet(remapped2, out var foundDesc2).Should().BeFalse();
+        Mod.Description.TryGetValue(remapped2, remapped2.IndexSegment, out var foundDesc2).Should().BeFalse();
     }
 
     [Fact]
@@ -1039,12 +1039,10 @@ public async Task CanGetAttributesThatRequireDI()
             Name = "Test Loadout",
             GamePath = path
         };
-        
+
         var result = await tx.Commit();
-
         var loadout = result.Remap(loadout1);
-
-        loadout.GamePath.Should().Be(path);
+        loadout.GamePath.Value.Should().Be(path);
     }
 
     [Fact]