将DateTime保存到Cassandra Date列 [英] Saving a DateTime to Cassandra Date column

问题描述

Cassandra .NET驱动程序文档令人难以置信，我试图拼凑一些功能，但是我浪费大量时间试图从发现的Java文档中更改代码。

Cassandra .NET driver documentation is unbelievably poor, I'm trying to scrap together something functional but I waste so much time trying to change code from Java documents that I found.

我正在尝试使用Cassandra驱动程序将数据写入一个简单的表中。该表格已经存在，并且里面有日期。我创建了一个映射并添加了一些列。以下是演示的简化版本：

I am trying to write data to a simple table using Cassandra driver. The table already exists and there's date inside. I have created a mapping and added some columns. Here's a cut-off version to demonstrate:

For<Profile>().TableName("profiles")
    .PartitionKey(p => p.IntegerId)
    .Column(p => p.IntegerId, cm => cm.WithName("profileid"))
    .Column(p => p.BirthDate, cm => cm.WithName("dateofbirth"))

更多列

然后通过简单的通用方法完成保存：

Then saving is done from a simple generic method:

public async Task<bool> Add<T>(T item) where T : EntityBase, new()
{
    await _mapper.InsertIfNotExistsAsync(item);
}

这里还有更多代码，但相关部分在这里。重要的是我正在使用InsertIfNotExists并使用与基础实体一起使用的通用方法。

Again there's more code there, but the relevant parts are here. What's important is that I'm using InsertIfNotExists and using generic method that works with a base entity.

dateofbirth 列在Cassandra中，日期类型。
当我运行Insert方法时，我得到一个例外，即Date的长度应该是4个字节而不是8个字节（我想我需要切断DateTime的时间部分）。

dateofbirth column in Cassandra is of type Date. When I run the Insert method I get exception that the length of Date should be 4 bytes instead of 8 (I assume I need to cut off the time part of the DateTime).

我尝试在映射上使用WithType并创建一个TypeSerializer，类似于在，但是没有运气。
任何人都有可以将这种类型（以及其他类型）保存到Cassandra的有效代码吗？

I tried using WithType on the mapping and creating a TypeSerializer similar to what was described at this question, but had no luck. Anyone has a working code that saves this type (and possibly other types) to Cassandra?

以下是从互联网改编的日期编解码器的代码，以及使用方式，可能（非常）错误：

Here's the code for the date codec that was adapted from the internet, and how it was used, it might be (very) wrong:

public class DateCodec : TypeSerializer<DateTime>
{
    private static TypeSerializer<LocalDate> _innerSerializer;

    public DateCodec(TypeSerializer<LocalDate> serializer)
    {
        _innerSerializer = serializer;
        TypeInfo = new CustomColumnInfo("LocalDate");
    }

    public override IColumnInfo TypeInfo { get; }

    public override DateTime Deserialize(ushort protocolVersion, byte[] buffer, int offset, int length, IColumnInfo typeInfo)
    {
        var result = _innerSerializer.Deserialize(protocolVersion, buffer, offset, length, typeInfo);
        return new DateTime(result.Year, result.Month, result.Day);
    }

    public override ColumnTypeCode CqlType { get; }

    public override byte[] Serialize(ushort protocolVersion, DateTime value)
    {
        return _innerSerializer.Serialize(protocolVersion, new LocalDate(value.Year, value.Month, value.Day));
    }
}

用法：

TypeSerializerDefinitions definitions = new TypeSerializerDefinitions();
definitions.Define(new DateCodec(TypeSerializer.PrimitiveLocalDateSerializer));

var cluster = Cluster.Builder()
    .AddContactPoints(...)
    .WithCredentials(...)
    .WithTypeSerializers(definitions)
    .Build();

推荐答案

C＃驱动程序使用 LocalDate 类代表Cassandra中的日期，因此要么需要更改您的 dateofbirth 声明即可使用

C# driver uses LocalDate class to represent date from Cassandra, so either need to change your declaration of dateofbirth to use it, or develop corresponding codec.

您可以查看C＃驱动程序的日期和时间表示文档：> https://docs.datastax.com/zh-CN/developer/csharp-driver/3.5/features/datatypes/ datetime /

You can check the documentation on date and time representation for the C# driver: https://docs.datastax.com/en/developer/csharp-driver/3.5/features/datatypes/datetime/

使用代码示例更新问题后进行更新：

Update after update of the question with code sample:

定义表&插入示例数据：

Define table & insert sample data:

cqlsh> create table test.dt(id int primary key, d date);
cqlsh> insert into test.dt(id, d) values(1, '2018-05-17');
cqlsh> insert into test.dt(id, d) values(2, '2018-05-16');
cqlsh> insert into test.dt(id, d) values(3, '2018-05-15');

为我转换的作品如下：

public class DateCodec : TypeSerializer<DateTime>
{
    private static readonly TypeSerializer<LocalDate> serializer = 
         TypeSerializer.PrimitiveLocalDateSerializer;

    public override ColumnTypeCode CqlType
    {
        get { return ColumnTypeCode.Date; }
    }

    public DateCodec() { }

    public override DateTime Deserialize(ushort protocolVersion, byte[] buffer, 
         int offset, int length, IColumnInfo typeInfo)
    {
        var result = serializer.Deserialize(protocolVersion, buffer,
                offset, length, typeInfo);
        return new DateTime(result.Year, result.Month, result.Day);
    }

    public override byte[] Serialize(ushort protocolVersion, DateTime value)
    {
        return serializer.Serialize(protocolVersion, 
            new LocalDate(value.Year, value.Month, value.Day));
    }
}

主程序：

TypeSerializerDefinitions definitions = new TypeSerializerDefinitions();
definitions.Define(new DateCodec());

var cluster = Cluster.Builder()
         .AddContactPoints("localhost")
         .WithTypeSerializers(definitions)
         .Build();
var session = cluster.Connect();
var rs = session.Execute("SELECT * FROM test.dt");
foreach (var row in rs)
{
    var id = row.GetValue<int>("id");
    var date = row.GetValue<DateTime>("d");
    Console.WriteLine("id=" + id + ", date=" + date);
}

var pq = session.Prepare("insert into test.dt(id, d) values(?, ?);");
var bound = pq.Bind(10, new DateTime(2018, 04, 01));
session.Execute(bound);

给出以下结果：

id=1, date=5/17/18 12:00:00 AM
id=2, date=5/16/18 12:00:00 AM
id=3, date=5/15/18 12:00:00 AM

然后从 cqlsh ：

cqlsh> SELECT * from test.dt ;

 id | d
----+------------
 10 | 2018-04-01
  1 | 2018-05-17
  2 | 2018-05-16
  3 | 2018-05-15

这篇关于将DateTime保存到Cassandra Date列的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！