当网格属性没有实体属性时，如何构建基于离网过滤的 LINQ predicate/dynamic.LINQ 查询？

Question

我有一个网格通过我的过滤器。所以我可能有一个 object 像：

var filter = new Filter(){
   Member = "Titles",
   Operator = Filter.Operators.IsEqualTo,
   Value = "Developer"
};

然后我需要使用它并扩展一个 IQueryable 以便做到这一点，我使用 dynamic.LINQ 并有一个方法来应用这些过滤器：

private IQueryable<TReportClass> ApplyFilter(ReportFilter filter, IQueryable<TReportClass> baseQuery)
    {
        switch (filter.Operator)
        {
            case ReportFilter.Operators.Contains:
                baseQuery = baseQuery.Where(string.Format("{0}.Contains(@0)", filter.Member), filter.Value);
                break;
            case ReportFilter.Operators.DoesNotContain:
                baseQuery = baseQuery.Where(string.Format("!{0}.Contains(@0)", filter.Member), filter.Value);
                break;
            case ReportFilter.Operators.IsEqualTo:
                baseQuery = baseQuery.Where(string.Format("{0} = @0", filter.Member), filter.Value);
                break;
            case ReportFilter.Operators.IsNotEqualTo:
                baseQuery = baseQuery.Where(string.Format("{0} != @0", filter.Member), filter.Value);
                break;
            case ReportFilter.Operators.StartsWith:
                baseQuery = baseQuery.Where(string.Format("{0}.StartsWith(@0)", filter.Member), filter.Value);
                break;
            case ReportFilter.Operators.EndsWith:
                baseQuery = baseQuery.Where(string.Format("{0}.EndsWith(@0)", filter.Member), filter.Value);
                break;
            case ReportFilter.Operators.IsNull:
                baseQuery = baseQuery.Where(string.Format("{0} = NULL", filter.Member));
                break;
            case ReportFilter.Operators.IsNotNull:
                baseQuery = baseQuery.Where(string.Format("{0} != NULL", filter.Member));
                break;
            case ReportFilter.Operators.IsEmpty:
                baseQuery = baseQuery.Where(string.Format("string.IsNullOrEmpty({0})", filter.Member));
                break;
            case ReportFilter.Operators.IsNotEmpty:
                baseQuery = baseQuery.Where(string.Format("!string.IsNullOrEmpty({0})", filter.Member));
                break;
        }

        return baseQuery;
    }

然而，这仅适用于 non-collections。我怎样才能让它与 collections 一起工作？如果我有这个模型：

public class UserReport : Entity
{
    public string Name { get; set; }
    public string Email { get; set; }
    public List<string> Titles { get; set; }
}

并将此查询作为基础：

IQueryable<UserReport> baseQuery = MyDbContext.DbSet<User>.Select(user => new UserReport
        {
            Id = user.Id,
            Name = user.FirstName + " " + user.LastName,
            Email = user.Email,
            Titles = user.Positions.Select(apptment => apptment.Title).ToList()
        })

所以我可以这样打电话：

IQueryable<UserReport> filteredQuery = ApplyFilters(filters, baseQuery);

如何将上述过滤器转换为 LINQ，例如：

baseQuery.Where(userReport => userReport.Titles.Any(title => title == "Developer")

这可以用动态 LINQ 完成吗？还是我需要构建自己的谓词？如果是这样，我该怎么做？

Answer 1

System.Linq.Dynamic 和 System.Linq.Expressions 都可以。

这是 System.Linq.Dynamic 的解决方案，以使其接近您当前的代码。您只需确定成员是否为 collection 并使用以下模式作为动态标准：

Collection: {PropertyName}.Any(it{condition})
Object: {PropertyName}{condition}

实现可能是这样的（基本上用 Func<string, string, string> 替换 string.Format）：

private IQueryable<TReportClass> ApplyFilter(ReportFilter filter, IQueryable<TReportClass> baseQuery)
{
    var property = typeof(TReportClass).GetProperty(filterMember);
    bool isCollection = property.Type != typeof(string) &&
        && typeof(IEnumerable).IsAssignableFrom(property.Type);
    Func<string, string, string> condtion;
    if (isCollection)
        condition = (format, member) => string.Format("{0}.Any({1})", member, string.Format(format, "it"));
    else
        condition = (format, member) => string.Format(format, member);
    switch (filter.Operator)
    {
        case ReportFilter.Operators.Contains:
            baseQuery = baseQuery.Where(condition("{0}.Contains(@0)", filter.Member), filter.Value);
            break;
        case ReportFilter.Operators.DoesNotContain:
            baseQuery = baseQuery.Where(condition("!{0}.Contains(@0)", filter.Member), filter.Value);
            break;
        case ReportFilter.Operators.IsEqualTo:
            baseQuery = baseQuery.Where(condition("{0} = @0", filter.Member), filter.Value);
            break;
        case ReportFilter.Operators.IsNotEqualTo:
            baseQuery = baseQuery.Where(condition("{0} != @0", filter.Member), filter.Value);
            break;
        case ReportFilter.Operators.StartsWith:
            baseQuery = baseQuery.Where(condition("{0}.StartsWith(@0)", filter.Member), filter.Value);
            break;
        case ReportFilter.Operators.EndsWith:
            baseQuery = baseQuery.Where(condition("{0}.EndsWith(@0)", filter.Member), filter.Value);
            break;
        case ReportFilter.Operators.IsNull:
            baseQuery = baseQuery.Where(condition("{0} = NULL", filter.Member));
            break;
        case ReportFilter.Operators.IsNotNull:
            baseQuery = baseQuery.Where(condition("{0} != NULL", filter.Member));
            break;
        case ReportFilter.Operators.IsEmpty:
            baseQuery = baseQuery.Where(condition("string.IsNullOrEmpty({0})", filter.Member));
            break;
        case ReportFilter.Operators.IsNotEmpty:
            baseQuery = baseQuery.Where(condition("!string.IsNullOrEmpty({0})", filter.Member));
            break;
    }

    return baseQuery;
}

当网格属性没有实体属性时，如何构建基于离网过滤的 LINQ predicate/dynamic.LINQ 查询？

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