用linq实现EFcore中的平坦化EFcore

Question

我试图在EF核心中扁平一个IEnumerable，但在SelectMany上出现了一个错误

public async Task<IEnumerable<WellDataTableViewModel>> GetWellsForDataTable() =>
            await context.Wells
            .Include(x => x.Pad)
            .ThenInclude(x => x.Tract)
            .Include(x => x.WellOperations)
            .ThenInclude(x => x.Lessee)
            .Select(p => new WellDataTableViewModel
             {
                WellId = p.Id,
                ApiNum = p.ApiNum,
                WellNum = p.WellNum,
                PadName = p.Pad.PadName,
                TractNum = p.Pad.Tract.TractNum,
                LesseeName = p.WellOperations.SelectMany(x => x.Lessee.LesseeName)
            })
            .ToListAsync().ConfigureAwait(false);

这是一个错误：

误差CS0266

无法隐式地将“System.Collections.Generic.IEnumerable”类型转换为“字符串”。存在显式转换(是否缺少强制转换？)

矿物C:\tfsmappings\Minerals-development\Minerals\Repositories\WellRepository.cs 33活性

下面是我试图填充的viewmodel类：

public class WellDataTableViewModel
{
        public long WellId { get; set; }
        public string WellNum { get; set; }
        public string ApiNum { get; set; }
        public string PadName { get; set; }
        public string TractNum { get; set; }
        public string LesseeName { get; set; }
}

WellOperations是油井上的IEnumerable，每一次井作业都有一个承租人，它持有string类型的lesseeName

在井班我有

public IEnumerable<WellOperation> WellOperations { get; set; }

在良好的操作中，我有一个承租人，它包含lesseeName

public class WellOperation
{
    public long Id { get; set; }
    public Single? OpShare { get; set; }
    public bool? ReportsTotal { get; set; }
    public string Notes { get; set; }
    public long? LesseeId { get; set; }
    public Lessee Lessee { get; set; }
    public long? WellId { get; set; }
    public Well Well { get; set; }
}

Answer 1

首先，不要使用Include(s)，如果您通过选择拥有完整的自定义投影，它们只会使LINQ查询解析复杂化：

public async Task<IEnumerable<WellDataTableViewModel>> GetWellsForDataTable()
{
    var query = 
       from w in context.Wells
       from wo in w.WellOperations
       select new WellDataTableViewModel
       {
          WellId = w.Id,
          ApiNum = w.ApiNum,
          WellNum = w.WellNum,
          PadName = w.Pad.PadName,
          TractNum = w.Pad.Tract.TractNum,
          LesseeName = wo.Lessee.LesseeName
        });

    return await query.ToListAsync();
}