Question

我有一个成功的查询，它将两个表与where和orderby子句链接起来，但我想添加到只选择特定列而不是让所有内容都恢复。

第1部分当我尝试这个时，我在orderby行上得到语法错误，如果我删除orderby行，语法错误会移动到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（您是否错过了演员？）

            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部分我还想知道我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，并且我在orderby行上获得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（您是否错过了演员？）

Answer 1

<强> ANSWER

我认为你帮助我偶然发现了类型不匹配的事实。制作IQueryable类型以及选择新类型和返回类型SAME使语法变得愉快。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;
}

Answer 2

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IQueryable<VendorProfileViewModel>，因为您要通过投影到VendorProfileViewModel来更改查询的形状。

实体框架 - 选择特定列

2 个答案: