EF Core Linq to SQLite 无法转换，可在 SQL Server 上运行

Question

我有一个 linq 表达式，它在生产数据库上运行良好，但在测试上下文的内存数据库中的 SQLite 上抛出错误。我得到的错误说：

The LINQ expression (EntityShaperExpression:

EntityType: Item
ValueBufferExpression: 
    (ProjectionBindingExpression: Inner)
IsNullable: True ).Price * (Nullable<decimal>)(decimal)(EntityShaperExpression: 
EntityType: ISItem
ValueBufferExpression: 
    (ProjectionBindingExpression: Outer)
IsNullable: False ).Qty' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.

linq 表达式：

var locationsQuery = context.DbContext.Locations
            .Include(x => x.Check)
            .Include(x => x.Scan)
            .Include(x => x.EScan)
                .ThenInclude(es => es!.Items)
                    .ThenInclude(isi => isi.Item)
            .Where(x => x.ProjectId == query.ProjectId)
            .Select(x => x);

然后我有一个预测：

LocationId = entity.Id,
        LHA = entity.LHA,
        Zone = entity.Zone,
        Area = entity.Area,
        LocationState = $"DB.{nameof(LocationState)}.{entity.State.ToString()}",
        CheckUserId = entity.Check != null ? entity.Check.ScanUserId : (int?)null,
        ScanUserId = entity.Scan != null ? entity.Scan.ScanUserId : (int?)null,
        CheckUserName = entity.Check != null ? entity.Check.ScanUser.Name : null,
        ScanUserName = entity.Scan != null ? entity.Scan.ScanUser.Name : null,
        SumPrice = entity.EffectiveScan != null // This cannot be evaluated
                        ? entity.EScan.Items
                            .Where(x => x.Item != null)
                            .Sum(x => x.Item!.Price * (decimal)x.Qty)
                        : null,
        SumQty = entity.EScan != null
                        ? entity.EScan.Items
                            .Sum(x => x.Qty)
                        : (double?)null

如果我删除 SumPrice 计算，它将按预期工作（与生产系统相同）。我可以对此查询做些什么，以便在 SqlServer 和 SQLite 内存数据库上同样工作？

Answer 1

您可能会在生产环境中使用除 sqllite 之外的某些数据库的代码。您可能不想根据对开发数据库的依赖关系来更改代码。在您的上下文类中，在 OnModelCreating 方法中添加以下代码片段并从代码中删除强制转换。

protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.ApplyConfigurationsFromAssembly(Assembly.GetExecutingAssembly());

        if (Database.ProviderName == "Microsoft.EntityFrameworkCore.Sqlite")
        {
            foreach (var entityType in modelBuilder.Model.GetEntityTypes())
            {
                var properties = entityType.ClrType.GetProperties().Where(p => p.PropertyType == typeof(decimal));
                var dateTimeProperties = entityType.ClrType.GetProperties()
                    .Where(p => p.PropertyType == typeof(DateTimeOffset));

                foreach (var property in properties)
                {
                    modelBuilder.Entity(entityType.Name).Property(property.Name).HasConversion<double>();
                }

                foreach (var property in dateTimeProperties)
                {
                    modelBuilder.Entity(entityType.Name).Property(property.Name)
                        .HasConversion(new DateTimeOffsetToBinaryConverter());
                }
            }
        }
    }