[backend/core] Use upsert for cache store instead of detecting conflicts (ISH-212)

Iceshrimp.Backend/Core/Services/CacheService.cs

@@ -147,21 +147,16 @@ public class CacheService([FromKeyedServices("cache")] DatabaseContext db)
 				Expiry = expiry,
 				Ttl    = ttl
 			};
-			db.Add(entity);
+
-			try
+			await db.CacheStore.Upsert(entity)
+			        .On(p => p.Key)
+			        .WhenMatched((_, orig) => new CacheEntry
 			        {
-				await db.SaveChangesAsync();
+				        Value  = orig.Value,
-			}
+				        Expiry = orig.Expiry,
-			catch (UniqueConstraintException)
+				        Ttl    = orig.Ttl
-			{
+			        })
-				db.Remove(entity);
+			        .RunAsync();
-				entity = await db.CacheStore.FirstOrDefaultAsync(p => p.Key == key) ??
-				         throw new Exception("Failed to fetch entity after UniqueConstraintException");
-				entity.Value  = value;
-				entity.Expiry = expiry;
-				entity.Ttl    = ttl;
-				await db.SaveChangesAsync();
-			}
 		}
 	}
 

Iceshrimp.Backend/Iceshrimp.Backend.csproj

@@ -25,6 +25,7 @@
         <PackageReference Include="dotNetRdf.Core" Version="3.2.6-iceshrimp"/>
         <PackageReference Include="EntityFrameworkCore.Exceptions.PostgreSQL" Version="8.0.0"/>
         <PackageReference Include="EntityFrameworkCore.Projectables" Version="3.0.4"/>
+        <PackageReference Include="FlexLabs.EntityFrameworkCore.Upsert" Version="8.0.0" />
         <PackageReference Include="Isopoh.Cryptography.Argon2" Version="2.0.0"/>
         <PackageReference Include="libsodium" Version="1.0.18.4"/>
         <PackageReference Include="Microsoft.AspNetCore.DataProtection.EntityFrameworkCore" Version="8.0.1"/>