应用表达式函数

Question

我需要用表达式参数实现过滤函数。 所以我无法将过滤后的查询应用于实体。

实体：

[XmlRoot(ElementName = "Zip")]
public class Zip
{
    [XmlAttribute(AttributeName = "code")]
    public string Code { get; set; }
}

[XmlRoot(ElementName = "District")]
public class District
{
    [XmlElement(ElementName = "Zip")]
    public List<Zip> Zip { get; set; }
    [XmlAttribute(AttributeName = "name")]
    public string Name { get; set; }
}

[XmlRoot(ElementName = "City")]
public class City
{
    [XmlElement(ElementName = "District")]
    public List<District> District { get; set; }
    [XmlAttribute(AttributeName = "name")]
    public string Name { get; set; }
    [XmlAttribute(AttributeName = "code")]
    public string Code { get; set; }
}

[XmlRoot(ElementName = "AddressInfo")]
public class AddressInfo
{
    [XmlElement(ElementName = "City")]
    public List<City> City { get; set; }
}

按城市名称＆＃34;柏林＆＃34;过滤的测试用例。如何在函数中应用谓词。

public IConverter<T> Filter(Expression<Func<T, bool>> predicate)
{
    // ???
    return this;
}

Answer 1

我认为您需要使用给定谓词过滤集合。

您可以定义一个Filter扩展方法，该方法将谓词作为参数（或者仅依赖于已存在的 collection.Where 扩展方法）

public static class Extensions
{
    public static IEnumerable<T> Filter<T>(this IEnumerable<T> collection, Func<T, bool> predicate)
    {
        return collection.Where(predicate);
    }
}

根据您的需求定义谓词

// Filter by city Berlin
Func<City, bool> berlin = city => city.Name == "Berlin";

// Filter by district Spandau
Func<City, bool> spandau = city => city.Districts.Any(d => d.Name == "Spandau");

// Filter by zip 10115
Func<City, bool> zipcode = city => 
{
    var predicate = from district in city.Districts
                    from zip in district.Zips
                    where zip.Code == "10115"
                    select zip;

    return predicate.Any();
};

根据给定的谓词

过滤数据

var query = from address in addresses
            from city in address.Cities.Filter(berlin)
            select city;