用导航属性替换连接

Question

根据这里人们的建议，我正在尝试使用导航属性重写下面的 linq 查询。

我还没有走多远，因为我不确定如何用导航属性替换我的 Linq 查询中的联接。

到目前为止，我有这个：

await _context.StarList(sl => new 
{
    sl.StarId,
    sl.StarType,
    sl.StarTitle,
    sl.ChemicalId...
}

但是，在原始查询中，我开始在查询中使用“化学原子”。

所以我不确定如何过渡到他们。

所以我的问题是，如何将原始查询中的联接替换为导航属性？

谢谢！

 public async Task<ActionResult<object>> GetStarChemicalData(string starID)
    {
        var starChemicalData = await (from starlist in _context.StarList
                                      join ql in _context.ChemicalList on starlist.ChemicalId equals ql.ChemicalId into stars
                                      from chemicallist in stars.DefaultIfEmpty()
                                      join qc in _context.ChemicalAtoms on chemicallist.ChemicalId equals qc.ChemicalId into chemicals
                                      from chemicalatoms in chemicals.DefaultIfEmpty()
                                      join nk in _context.StarLinks on chemicalatoms.AtomId equals nk.AtomId into links
                                      from starlinks in links.DefaultIfEmpty()
                                      where starlist.StarId == starID
                                      select new
                                      {
                                          StarId = starlist.StarId,
                                          StarType = starlist.StarType,
                                          StarTitle = starlist.StarTitle,
                                          ChemicalId = starlist.ChemicalId,
                                          AtomId = (Guid?)chemicalatoms.AtomId,
                                          OrderId = chemicalatoms.OrderId,
                                          ChemicalText = chemicallist.ChemicalText,
                                          AtomText = chemicalatoms.AtomText,
                                          Wavelength = chemicalatoms.Wavelength,
                                          isRedShifted = (starlinks.AtomId != null && starlist.StarType == 1) ? 1
                                          : (starlinks.AtomId == null && starlist.StarType == 1) ? 0
                                          : (int?)null
                                      })
                                          .GroupBy(x => x.StarId)
                                          .Select(g => new
                                          {
                                              StarId = g.FirstOrDefault().StarId,
                                              StarType = g.FirstOrDefault().StarType,
                                              StarTitle = g.FirstOrDefault().StarTitle,
                                              ChemicalId = g.FirstOrDefault().ChemicalId,
                                              ChemicalText = g.FirstOrDefault().ChemicalText,
                                              ChemicalAtoms = (g.FirstOrDefault().AtomId != null ? g.Select(x => new
                                              {
                                                  AtomId = x.AtomId,
                                                  OrderId = x.OrderId,
                                                  AtomText = x.AtomText,
                                                  Feedback = x.Wavelength,
                                                  IsCorrect = x.isRedShifted
                                              }) : null)
                                          }).FirstOrDefaultAsync();

        return starChemicalData;
        

Answer 1

根据上面的通信成功，我想我可以总结一下结果，这里)) 所以，不要这样：

var starChemicalData = await (from starlist in _context.StarList
    join ql in _context.ChemicalList on starlist.ChemicalId equals ql.ChemicalId into stars
    from chemicallist in stars.DefaultIfEmpty()
    join qc in _context.ChemicalAtoms on chemicallist.ChemicalId equals qc.ChemicalId into chemicals
    from chemicalatoms in chemicals.DefaultIfEmpty()
    join nk in _context.StarLinks on chemicalatoms.AtomId equals nk.AtomId into links 
    ...
    );

我们可以这样：

_context.StarList.Include(st => st.ChemicalList)
    .Include(ca => ca.ChemicalAtoms)  // or ThenInclude, based on your relations
    .Include(sl => sl.StartLinks)
    ...
    Select(r => new {...})
    ...

---

请注意，使用Include 时最重要的是您的关系（主外键）应该在您在此处使用的数据库表之间进行适当设置。

另一个重要的事情是，如果您的 PK⟶FK 关系中的一个包含 null 值，Include() 将不会带来行结果，而实际上它不应该。