Neo4j能否在节点中存储字典？

Question

Neo4j能否在节点中存储字典？

5

我正在使用C#并且使用neo4jclient。我知道如果我向neo4jclient传递一个类对象，它可以创建一个节点（我已经尝试过了）。现在在我的类中，我想添加一个字典属性，但是这样做不起作用。我的代码：

 GraphClient client = getConnection();
 client.Cypher
       .Merge("(user:User { uniqueIdInItsApp: {id} , appId: {appId} })")
       .OnCreate()
       .Set("user = {newUser}")
       .WithParams(new
       {
           id = user.uniqueIdInItsApp,
           appId = user.appId,
           newUser = user
       })
       .ExecuteWithoutResults();

User 在 C# 中包含一个属性，它是一个 Dictionary。当执行cypher时，会显示错误。

MatchError: Map() (of class scala.collection.convert.Wrappers$JMapWrapper)

有没有人能帮助我？

- user2234995

1个回答

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- Charlotte Skardon · Accepted Answer

默认情况下，Neo4j不处理字典（Java中的Maps），所以你唯一的解决方案是使用自定义序列化器，将字典序列化为字符串属性...

以下代码仅适用于给定的类型，您需要做类似的事情，以便尽可能使用默认处理，并仅对您的类型使用此转换器：

//This is what I'm serializing
public class ThingWithDictionary
{
    public int Id { get; set; }
    public IDictionary<int, string> IntString { get; set; }
}

//This is the converter
public class ThingWithDictionaryJsonConverter : JsonConverter
{
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var twd = value as ThingWithDictionary;
        if (twd == null)
            return;

        JToken t = JToken.FromObject(value);
        if (t.Type != JTokenType.Object)
        {
            t.WriteTo(writer);
        }
        else
        {
            var o = (JObject)t;
            //Store original token in a temporary var
            var intString = o.Property("IntString");
            //Remove original from the JObject
            o.Remove("IntString");
            //Add a new 'InsString' property 'stringified'
            o.Add("IntString", intString.Value.ToString());
            //Write away!
            o.WriteTo(writer);
        }
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (objectType != typeof(ThingWithDictionary))
            return null;

        //Load our object
        JObject jObject = JObject.Load(reader);
        //Get the InsString token into a temp var
        var intStringToken = jObject.Property("IntString").Value;
        //Remove it so it's not deserialized by Json.NET
        jObject.Remove("IntString");

        //Get the dictionary ourselves and deserialize
        var dictionary = JsonConvert.DeserializeObject<Dictionary<int, string>>(intStringToken.ToString());

        //The output
        var output = new ThingWithDictionary();
        //Deserialize all the normal properties
        serializer.Populate(jObject.CreateReader(), output);

        //Add our dictionary
        output.IntString = dictionary;

        //return
        return output;
    }

    public override bool CanConvert(Type objectType)
    {
        //Only can convert if it's of the right type
        return objectType == typeof(ThingWithDictionary);
    }
}

然后在Neo4jClient中使用：

var client = new GraphClient(new Uri("http://localhost:7474/db/data/"));
client.Connect();
client.JsonConverters.Add( new ThingWithDictionaryJsonConverter());

当可用时，它将使用该转换器。