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我有一个成功的查询，它将两个表与 where 和 orderby 子句联系起来，但我想添加以仅选择特定列而不是取回所有内容。

第 1 部分当我尝试这样做时，我在 orderby 行上出现语法错误，如果我删除 orderby 行，语法错误将移至 where 行。

错误 3 无法将类型“System.Linq.IOrderedQueryable”隐式转换为“System.Linq.IQueryable”。存在显式转换（您是否缺少演员表？） 

            IQueryable<VendorProfile> query = _db.VendorProfiles
            .Include("VendorCategories")
            .Include("VendorsSelected")
            .Select(s => new  { s.ProfileID, s.Name, s.CompanyName, s.City, s.State, s.DateCreated, s.VendorsSelected, s.VendorCategories })
            .Where(x => x.VendorsSelected.Select(s => s.UserName).Contains(HttpContext.Current.User.Identity.Name))
            .OrderBy(x => x.DateCreated);

       if (criteria.name != string.Empty)
            query = query.Where(v => v.Name.Contains(criteria.name));
        if (criteria.company != string.Empty)
            query = query.Where(v => v.CompanyName.Contains(criteria.company));
        if (criteria.startDate != null && criteria.endDate != null)
            query = query.Where(v => v.DateCreated > criteria.startDate && v.DateCreated < criteria.endDate);
        if (criteria.categories != null && !criteria.categoryMatchAll)
            query = query.Where(v => criteria.categories.AsQueryable().Any(cat => v.VendorCategories.Select(vendCat => vendCat.CategoryID).Contains(cat)));
        if (criteria.categories != null && criteria.categoryMatchAll)
            query = query.Where(v => criteria.categories.AsQueryable().All(cat => v.VendorCategories.Select(vendCat => vendCat.CategoryID).Contains(cat)));
        if (criteria.minorityType != null)
            query = query.Where(v => v.MinotiryOwned == criteria.minorityType);
        if (criteria.diversityClass != null)
            query = query.Where(v => v.DiversityClassification == criteria.diversityClass);

        return query.ToList();

第 2 部分我还想知道是否可以将选定的列提取到视图模型类中，所以我厌倦了这个，我在 orderby 行上得到了与上面相同的结果

错误 4 无法将类型“System.Linq.IOrderedQueryable”隐式转换为“System.Linq.IQueryable”。存在显式转换（您是否缺少演员表？）

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2 回答 2

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回答

我认为您帮助我偶然发现了类型不匹配的事实。使 IQueryable 类型和选择新类型以及返回类型 SAME 使语法快乐。使用 var 不喜欢。

public IEnumerable<BrowseVendorModel> SearchVendors(CustomSearchModel criteria)
{
    IQueryable<BrowseVendorModel> query = _db.VendorProfiles
        .Include("VendorCategories")
        .Include("VendorsSelected")
        .Select(s => new BrowseVendorModel
        {
            ProfileID = s.ProfileID,
            Name = s.Name,
            CompanyName = s.CompanyName,
            City = s.City,
            State = s.State,
            DateCreated = s.DateCreated,
            VendorsSelected = s.VendorsSelected,
            VendorCategories = s.VendorCategories
        })
        .Where(x => x.VendorsSelected.Select(s => s.UserName).Contains(HttpContext.Current.User.Identity.Name))
        .OrderBy(x => x.DateCreated);

    if (criteria.name != string.Empty)
        query = query.Where(v => v.Name.Contains(criteria.name));
    if (criteria.company != string.Empty)
        query = query.Where(v => v.CompanyName.Contains(criteria.company));
    if (criteria.startDate != null && criteria.endDate != null)
        query = query.Where(v => v.DateCreated > criteria.startDate && v.DateCreated < criteria.endDate);
    if (criteria.categories != null && !criteria.categoryMatchAll)
        query = query.Where(v => criteria.categories.AsQueryable().Any(cat => v.VendorCategories.Select(vendCat => vendCat.CategoryID).Contains(cat)));
    if (criteria.categories != null && criteria.categoryMatchAll)
        query = query.Where(v => criteria.categories.AsQueryable().All(cat => v.VendorCategories.Select(vendCat => vendCat.CategoryID).Contains(cat)));
    if (criteria.minorityType != null)
        query = query.Where(v => v.MinotiryOwned == criteria.minorityType);
    if (criteria.diversityClass != null)
        query = query.Where(v => v.DiversityClassification == criteria.diversityClass);

    return query;
}
于 2013-03-21T17:02:19.700 回答
0

第一个示例需要var，因为您通过投影到匿名类型来更改查询的形状。第二个示例可以使用var，或者IQueryable<VendorProfileViewModel>因为您通过投影来更改查询的形状VendorProfileViewModel。

于 2013-03-20T19:30:48.613 回答