c# - 如何将 AddRange 添加到字典但过滤掉空键？

Question

此问题中的代码生成以下 JSON。

代码应该根据 .Where(a => a.Values != null) 行排除空的“子”键，但它不起作用。

我可以在哪里放置 where 子句，以便 JSON 不包含一堆空的“子”数组？

感谢您的帮助。

[{
        "NodeID" : 1,
        "NodeText" : "Country",
        "Children" : [{
                "NodeID" : 3,
                "NodeText" : "President",
                "Children" : []
            }, {
                "NodeID" : 4,
                "NodeText" : "Population",
                "Children" : []
            }, {
                "NodeID" : 5,
                "NodeText" : "State",
                "Children" : [{
                        "NodeID" : 6,
                        "NodeText" : "Governor",
                        "Children" : []
                    }, {
                        "NodeID" : 7,
                        "NodeText" : "Population",
                        "Children" : []
                    }, {
                        "NodeID" : 8,
                        "NodeText" : "County",
                        "Children" : [{
                                "NodeID" : 9,
                                "NodeText" : "Population",
                                "Children" : []
                            }
                        ]
                    }
                ]
            }
        ]
    }, {
        "NodeID" : 2,
        "NodeText" : "Year",
        "Children" : []
    }
]

下面是生成上述 JSON 的示例代码:

public class Node
{
    public int? ParentNodeID { get; set; }
    public int NodeID { get; set; }
    public string NodeText { get; set; }

    public Node(int? parentNodeID, int nodeID, string nodeText)
    {
        ParentNodeID = parentNodeID;
        NodeID = nodeID;
        NodeText = nodeText;
    }
}

public List<Dictionary<string, object>> BuildTree(int? parentNodeID = null, List<Node> exampleData = null)
{
    // kickstart the recursion with example data
    if (exampleData == null)
    {
        exampleData = new List<Node>();
        exampleData.Add(new Node(null, 1, "Country"));
        exampleData.Add(new Node(null, 2, "Year"));
        exampleData.Add(new Node(1, 3, "President"));
        exampleData.Add(new Node(1, 4, "Population"));
        exampleData.Add(new Node(1, 5, "State"));
        exampleData.Add(new Node(5, 6, "Governor"));
        exampleData.Add(new Node(5, 7, "Population"));
        exampleData.Add(new Node(5, 8, "County"));
        exampleData.Add(new Node(8, 9, "Population"));
    }

    List<Dictionary<string, object>> result = new List<Dictionary<string, object>>();

    var nodes = exampleData.Where(a => a.ParentNodeID == parentNodeID).ToList();

    if (nodes != null)
    {
        result.AddRange(nodes
            .Select(a => new Dictionary<string, object> {
                { "NodeID", a.NodeID},
                { "NodeText", a.NodeText },
                { "Children", BuildTree(a.NodeID, exampleData) }
            })
            .Where(a => a.Values != null) // this doesn't have any effect
            .ToList()
        );
    }
    return result;
}

Answer 1

问题是您总是创建一个包含值“Children”的字典，即使没有子项也是如此。

解决方案是将其放入一个条件中，如果没有 child 则不添加该值，否则无论如何您都会继续添加具有空集合值的 Children Key。

这是我用来完成此任务的代码:肉和土 bean 是 Func<T> getNodeDictionary现在在递归语句中调用。

    public static List<Dictionary<string, object>> BuildTree(int? parentNodeID = null, List<Node> exampleData = null)
    {
        // kickstart the recursion with example data
        if (exampleData == null)
        {
            exampleData = new List<Node>();
            exampleData.Add(new Node(null, 1, "Country"));
            exampleData.Add(new Node(null, 2, "Year"));
            exampleData.Add(new Node(1, 3, "President"));
            exampleData.Add(new Node(1, 4, "Population"));
            exampleData.Add(new Node(1, 5, "State"));
            exampleData.Add(new Node(5, 6, "Governor"));
            exampleData.Add(new Node(5, 7, "Population"));
            exampleData.Add(new Node(5, 8, "County"));
            exampleData.Add(new Node(8, 9, "Population"));
        }

        List<Dictionary<string, object>> result = new List<Dictionary<string, object>>();

        var nodes = exampleData.Where(a => a.ParentNodeID == parentNodeID).ToList();

        if (nodes != null)
        {
            Func<Node, Dictionary<string, object>> getNodeDictionary = n => {
                var children = BuildTree(n.NodeID, exampleData); // still recursive
                var returnDictionary = new Dictionary<string, object> { // these 2 nodes always get added
                    { "NodeID", n.NodeID},
                    { "NodeText", n.NodeText }
                };

                // This ensures we only add Children if there are actually any children
                if (children.Any())
                {
                    returnDictionary.Add("Children", children);
                }

                return returnDictionary;
            };

            // No need for where clause since we now do not add the empty elements
            result.AddRange(nodes
                .Select(a => getNodeDictionary(a))
                .ToList()
            );
        }

        return result;
    }