ElasticSearch 2.X升级到6.X遇到的几个问题

1.IndexExists检测索引是否存在，更简洁了，可以这样

_ElasticClient.IndexExists(indices : indexName).Exists

2.索引数据的时候，如果数据是个字符串json，那么索引后查看数据是有问题的，索引的数据需要是个Model对象，此情况是个人遇到的，不确定是否有其他操作方法

3.如果索引数据是做了路由处理的话，那么使用Id搜索或者删除也必须加上路由信息，不然会404找不到的，此情况只针对Id搜索或删除

_ElasticClient.Get(new DocumentPath<T>(esId), s => s.Type(_EsType).Routing(routing))

_ElasticClient.DeleteAsync(new DeleteRequest(_ElasticClient.ConnectionSettings.DefaultIndex, _EsType, esId) { Routing = routing });

4.es.dll 6.x的使用虽然摆脱了Newtonsoft.Json的依赖，但也出现一些新的问题，序列化会和Newtonsoft不太一样，导致老项目无法直接使用，比如c# Model中的属性“Name”标记了jsonproperty["nm"],但6.x中索引的数据并没有使用nm，依然是Name，这就是6.x中自带序列化的问题。对于这个情况，6.x其实提供了一个接口IElasticsearchSerializer，只需要去实现并且使用即可，使用方法如下

var _ConnectionPool = new StaticConnectionPool(uris);
var _ConnectionConfig = new ConnectionSettings(_ConnectionPool, sourceSerializer: (builtin, settingss) => new JsonNetSerializer());
var _ElasticClient = new ElasticClient(_ConnectionConfig.DefaultIndex("IndexName").DefaultFieldNameInferrer((name) => name));

　JsonNetSerializer 是新建的实现类，继承IElasticsearchSerializer，实现如下

public class JsonNetSerializer : IElasticsearchSerializer
{
    private static JsonSerializer serializer = JsonSerializer.CreateDefault();
    private static JsonSerializer indentedSerializer =
        JsonSerializer.CreateDefault(new JsonSerializerSettings
        {
            Formatting = Newtonsoft.Json.Formatting.Indented
        });

    public object Deserialize(Type type, Stream stream)
    {
        var streamReader = new StreamReader(stream);
        var reader = new JsonTextReader(streamReader);
        return serializer.Deserialize(reader, type);
    }

    public T Deserialize<T>(Stream stream)
    {
        return (T)Deserialize(typeof(T), stream);
    }

    public Task<object> DeserializeAsync(Type type, Stream stream, CancellationToken cancellationToken = default(CancellationToken))
    {
        var o = Deserialize(type, stream);
        return Task.FromResult(o);
    }

    public Task<T> DeserializeAsync<T>(Stream stream, CancellationToken cancellationToken = default(CancellationToken))
    {
        var o = Deserialize<T>(stream);
        return Task.FromResult(o);
    }

    public void Serialize<T>(T data, Stream stream, SerializationFormatting formatting = SerializationFormatting.Indented)
    {
        var writer = new StreamWriter(stream);
        if (formatting == SerializationFormatting.Indented)
            indentedSerializer.Serialize(writer, data, typeof(T));
        else
            serializer.Serialize(writer, data, typeof(T));    

        writer.Flush();
    }

    public Task SerializeAsync<T>(T data, Stream stream, SerializationFormatting formatting = SerializationFormatting.Indented, CancellationToken cancellationToken = default(CancellationToken))
    {
        Serialize(data, stream, formatting);
        return Task.CompletedTask;
    }
}