Returning multiple columns in Neo4jClient Cypher Query

问题

I am using Azure and finding the performance to be slow. In order to reduce the round trip time, I am clubbing the following queries into one query.

var queryItem = _graphClient
            .Cypher
            .Start(new
            {
                n = Node.ByIndexLookup("item_idx", "SKU", sSKU1),
            })
             .Return<Node<Item>>("n");

somewhere else in the code I have following statements

var queryItem = _graphClient
            .Cypher
            .Start(new
            {
                m = Node.ByIndexLookup("item_idx", "SKU", sSKU2),
            })
             .Return<Node<Item>>("m");

I tried to combine above two queries into a single query like this

var queryItem = _graphClient
            .Cypher
            .Start(new
            {
                n = Node.ByIndexLookup("item_idx", "SKU", sSKU1),
                m = Node.ByIndexLookup("item_idx", "SKU", sSKU2),
            })
             .Return<Node<Item>>("n");

I know above is only for single column so I tried using following return statement

.Return((n, m) => new
        {
            N = n.CollectAs<Node<Item>>(),
            M = m.CollectAs<Node<Item>>()
        });

but then I have problems with the following statement

Node<Item> item1 = itemQueryResult.First();

It says Error Cannot implicitly convert type 'AnonymousType#1' to 'Neo4jClient.Node.

Can you please suggest a simple syntax or returning multiple columns and a way to extract the first node? TIA.

回答1:

I think what you're missing here is that the Return statement returns one object per Cypher row.

Your query is returning a table like this:

|-----------------|
|    n   |   m    |
|-----------------| 
|  Node  |  Node  |
|------------------

That's one table, with one row, with two columns.

In this statement, you are returning an anonymous type per Cypher row:

.Return((n, m) => new
{
    N = n.CollectAs<Node<Item>>(),
    M = m.CollectAs<Node<Item>>()
});

The return type of that method is IEnumerable<AnonymousType>.

You're then trying to get the first row (an anonymous type) and implicitly cast that to Node<Item>, which is not valid.

You should get the row, then get the properties within it.

Some other things to note:

You don't want to use CollectAs in this scenario: that will turn each cell of your table into an array with a single value, which just adds more indirection.
.As<Node<T>>() can be written as .Node<T>()

With that in mind, here's the query you want:

var result = _graphClient
    .Cypher
    .Start(new
    {
        n = Node.ByIndexLookup("item_idx", "SKU", sSKU1),
        m = Node.ByIndexLookup("item_idx", "SKU", sSKU2),
    })
    .Return((n, m) => new
    {
        N = n.Node<Item>(),
        M = m.Node<Item>()
    })
    .Results
    .Single();

var n = result.N;
var m = result.M;

Make sense?

PS: I hope you aren't actually clubbing anything. Baby seals don't like that. You are combining queries.

来源：https://stackoverflow.com/questions/16431716/returning-multiple-columns-in-neo4jclient-cypher-query

标签

neo4jclient