Neo4jClient-从Cypher查询中检索关系 [英] Neo4jClient - Retrieving relationship from Cypher query

问题描述

我无法从Cypher查询中检索匹配的关系。

I'm having trouble retrieving matched relationships from a Cypher query.

我有这个简单的试用代码：

I have this simple trial code:

var movie = client.Create(new Movie { Title = "The Matrix" });

client.Create(new Actor { Name = "Keanu Reeves" },
    new ActedIn(movie, new ActedInPayload { Role = "Neo" }));

client.Create(new Actor { Name = "Hugo Weaving" },
    new ActedIn(movie, new ActedInPayload { Role = "Agent Smith" }));

var actorsAndRoles = client
    .Cypher
    .Start(new { movie = movie })
    .Match("actor-[r:ACTED_IN]->movie")
    .Return((actor, r) => new
    {
        Actor = actor.As<Node<Actor>>()
        // ActedIn = r.As<?????>()
    })
    .Results;

问题是我不知道如何转换r（具有匹配关系）。

Problem is that I can't work out how to cast the r (with the matched relationship).

尝试了各种 .As类型强制转换，但没有效果。由于我的关系类没有无参数的构造函数，因此强制转换为Relations无效。但是，Relationships基类本身没有无参数的构造函数，因此不要认为这可行。另一方面，强制转换为RelationshipReference会导致异常。完全不进行强制转换（仅返回r）会导致不支持异常。

Tried various ".As" type casts, but none work. Casting to Relationship doesn't work because my relationship class doesn't have a parameterless constructor - but then the Relationship base class doesn't have a parameterless constructor itself, so don't think that would work. Casting to RelationshipReference on the other hand causes an exception. Not casting at all (just returning r) causes a "not supported" exception.

有一些与此相关的SO条目，但是那里的建议代码不再

There are some related SO entries about this issue, but the suggested code there either no longer works or is deprecated.

如何检索匹配的关系？

推荐答案

您可以为您的关系类型创建一个无参数的构造函数，只需将其 duff数据传递给它，我知道听起来很糟糕，但是由于您实际上并不需要它，所以不会伤害了您：

You can create a parameterless constructor for your relationship type, you just pass it 'duff' data, which I know sounds bad, but as you don't really need it, it won't hurt you:

public class ActedIn : Relationship<ActedInPayload>, IRelationshipAllowingSourceNode<Actor>, IRelationshipAllowingTargetNode<Movie>
{
    public ActedIn() : base(-1, null) {}
    public ActedIn(NodeReference targetNode, ActedInPayload data) : base(targetNode, data) {}

    public override string RelationshipTypeKey
    {
        get { return "ACTED_IN"; }
    }
}

所以这是 ActedIn 类，无参数构造函数将 -1链接到基本构造函数。

So this is the ActedIn class, with the parameterless constructor chaining a '-1' down to the base constructor.

您的查询将变为：

var actorsAndRoles = client
    .Cypher
    .Start(new {movie})
    .Match("actor-[r:ACTED_IN]->movie")
    .Return((actor, r) => new
        {
            Actor = actor.As<Node<Actor>>(),
            ActedIn = r.As<RelationshipInstance<ActedInPayload>>()
        })
    .Results;

注意，它被强制转换为类型为<$的 RelationshipInstance c $ c> ActedInPayload 不 ActedIn ，然后，获取您可能想要的数据：

Note, it's being cast to a RelationshipInstance of type ActedInPayload not ActedIn, then, to get the data you might want:

foreach (var actorsAndRole in actorsAndRoles)
{
    Console.WriteLine("{0} acted as {1} - which is in the db as {2}-[ACTED_IN]->{3}", 
        actorsAndRole.Actor.Data.Name, 
        actorsAndRole.ActedIn.Data.Role, 
        actorsAndRole.ActedIn.StartNodeReference.Id, 
        actorsAndRole.ActedIn.EndNodeReference.Id);
}

哪个会给你类似的东西：

Which will give you something like:

Keanu Reeves担任Neo-在数据库中为482- [ACTED_IN]-> 481

Keanu Reeves acted as Neo - which is in the db as 482-[ACTED_IN]->481

Hugo Weaving担任Agent Smith-在数据库中为483- [ACTED_IN]-> 481

Hugo Weaving acted as Agent Smith - which is in the db as 483-[ACTED_IN]->481

尽管在您自己的数据库中显然有不同的数字。

Though obviously with different numbers on your own DB.

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