c# - .net mvc - 如何使类方法参数 (IQueryable) 可以为空

Question

我有一个接收可查询参数的类方法:

public IQueryable<Company> getEmpresasVisiblesUsuario(IQueryable<Company> companies, bool onlyActive = true)
{
    /*
    if (companies == null) {
        companies = db.companies;
    }
    */

    int userId = HttpContext.Current.User.Identity.GetUserId<int>();
    companies = companies.Where(s => s.id_user == userId);

    if (onlyActive) {
        companies = companies.Where(e => e.active);
    }   
    return companies;
}

这工作正常，但现在我需要参数“companies”是可选的……我该怎么做？ 我试过 IQueryable？公司，但这给出了一个错误:

the type IQueryable<Company> must be a non-nullable value type in order to use it as a parameter 'T' in the generic type or method 'Nullable<T>'

Answer 1

您可以重载您的方法:

public IQueryable<Company> getEmpresasVisiblesUsuario(bool onlyActive = true)
{
     return getEmpresasVisiblesUsuario(db.companies, onlyActive);
}

public IQueryable<Company> getEmpresasVisiblesUsuario(IQueryable<Company> companies, bool onlyActive = true)
{
    int userId = HttpContext.Current.User.Identity.GetUserId<int>();
    companies = companies.Where(s => s.id_user == userId);

    if (onlyActive) {
        companies = companies.Where(e => e.active);
    }   
    return companies;
}