Question

比方说我有一个List<Person>，其中每个人都有十几个属性。生成列表时，前十个属性都已设置。

稍后我需要填充列表中每个项目的最后两个属性的数据。

我有一个返回PersonId，Property11，Property12的存储过程，我想使用Linq从IDataReader获取值，并从列表中填充正确Person的值，显然在PersonId上匹配。

我从以下开始:(这不是我正在使用的实际代码，但结构类似。）

public void GetAdditionalProps( List<IPersonData> people)
{
    var peopleIds = String.Join( ",", people.Select(x => x.ID));

    using (var conn = Database.GetConnection(Database.PeopleDB))
    {
        conn.Open();
        using (var cmd = conn.CreateCommand())
        {
            cmd.CommandText = "spGetPeopleData" ;
            cmd.CommandType = CommandType.StoredProcedure;

            cmd.AddParameterWithValue( "@Ids" , peopleIds);

            using (var reader = cmd.ExecuteReader())
            {
                while (reader.Read())
                {
                    var pd = people.First(p => p.ID.Equals(reader["PersonId" ]));
                    pd.HairColor = reader["HairColor" ].ToString();
                    pd.EyeColor = reader["EyeColor" ].ToString();
                }
            }
        }
    }
}

但我想知道我是否可以使用Linq来填充每个列表项的数据而无需单独找到每个列表项？

Answer 1

你可以这样做......

虽然没有多少使用＆＃34;强迫＆＃34; Linq在这里......

也许加入比每次调用First（）更快......

public Tuple<int,string,string> GetAdditionalData(List<IPersonData> people)
{
    string peopleIds = String.Join( ",", people.Select(x => x.ID));

    using (var conn = Database.GetConnection(Database.PeopleDB))
    {
        conn.Open();
        using (var cmd = conn.CreateCommand())
        {
            cmd.CommandText = "spGetPeopleData" ;
            cmd.CommandType = CommandType.StoredProcedure;

            cmd.AddParameterWithValue( "@Ids" , peopleIds);

            using (var reader = cmd.ExecuteReader())
            {
                while (reader.Read())
                {
                    yield return new Tuple<int,string,string>(
                        reader["PersonId" ],
                        reader["HairColor" ],
                        reader["EyeColor" ]);
                }
            }
        }
    }
}

public void Enrich(List<IPersonData> people)
{
    var dataToEnrich = from person in people
                       join additional in GetAdditionalData(people)
                           on additional.Item1 equals person.ID
                       select new { Person = person, 
                                    HairColor = additional.Item2, 
                                    EyeColor = additional.Item3 };

    foreach(var enrichment in dataToEnrich)
    {
        enrichment.Person.HairColor = enrichment.HairColor;
        enrichment.Person.EyeColor = enrichment.EyeColor ;
    }
}

我可以使用Linq从数据读取器</object>设置List <object>的属性

1 个答案: