F# - 具有多个返回值的密码查询

Question

鉴于此查询(来自 here )

  let pAfollowers =
        client.Cypher
            .Match("n<-[:follows]-e")
            .Where(fun n -> n.Twitter = "tA")
            .Return<Person>("e")
            .Results
            .Select(fun x -> x.Name)

我想调整它并让它返回打包在一起的多个值。
不确定类型应该如何显示:

let pAfollowers =
        client.Cypher
            .Match("n<-[r:follows]-e")
            .Where(fun n -> n.Twitter = "tA")
            .Return<???>("n, r, e")

其次，我想知道是否有可能在 CreateUnique 之后有一个 return 语句。 .
我正在尝试调整此查询:

let knows target (details : Knows) source =
        client.Cypher
            .Match("(s:Person)", "(t:Person)")
            .Where(fun s -> s.Twitter = source.Twitter)
            .AndWhere(fun t -> t.Twitter = target.Twitter)
            .CreateUnique("s-[:knows {knowsData}]->t")
            .WithParam("knowsData", details)
            .ExecuteWithoutResults()

让它返回 s , t和 details .

Answer 1

好的，好消息/坏消息 - 尽管在实践中好与坏相结合:(

先说好:

您可以在 CreateUnique 之后返回，例如:

.CreateUnique("s-[:Knows {knowsData}]-t")
.WithParam("knowsData", details)
.Returns<???>( "s,t" )
.Results;

坏消息:

坏消息是您可能无法在 F# 中做到这一点。 Neo4jClient要求您使用对象初始值设定项或匿名类型来转换数据，因此您可以尝试以下操作:

type FollowingResults = { Follower : Person; Followed : Person;}

let createExpression quotationExpression = LeafExpressionConverter.QuotationToLambdaExpression quotationExpression

let pAfollowers =
    client.Cypher
        .Match("n<-[:follows]-e")
        .Where(fun n -> n.Twitter = "tA")
        .Return(createExpression <@ Func<ICypherResultItem, ICypherResultItem, FollowingResults>(fun (e : Cypher.ICypherResultItem) (n : Cypher.ICypherResultItem) -> {Follower = e.As<Person>(); Followed = n.As<Person>()}) @>)
        .Results
        .Select(fun x -> x)

for follower in pAfollowers do
    printfn "%s followed %s" follower.Follower.Name follower.Followed.Name

F# 编译器对此完全没有问题。然而， Neo4jClient将抛出带有以下消息的 Argument 异常:

The expression must be constructed as either an object initializer (for example: n => new MyResultType { Foo = n.Bar }), an anonymous type initializer (for example: n => new { Foo = n.Bar }), a method call (for example: n => n.Count()), or a member accessor (for example: n => n.As().Bar). You cannot supply blocks of code (for example: n => { var a = n + 1; return a; }) or use constructors with arguments (for example: n => new Foo(n)).

问题是，F# 没有对象初始值设定项，也没有匿名类型，您可以与 F# 的东西纠缠多年而无处可去，因为 C# 无法识别 F# 初始化。