使用Json.NET测试嵌套键?
我想过滤一个json编码字符串的反应流,如下所示:
{ "Key1" : {"key2":"value"}, "key3" : "other values" }
我想过滤具有key2
值的项目,如下所示:
IDisposable valueQuery = globalEventStream .Select(e => JObject.Parse(e.EventArgs.Data)) .Where(e => e["key1"]["key2"] != null)
但这给了我错误
Cannot access child value on Newtonsoft.Json.Linq.JValue
我能找到解决这个问题的唯一方法是执行以下操作:
IDisposable deathDisposable = globalEventStream .Select(e => JObject.Parse(e.EventArgs.Data)) .Where(e => e["key1"] != null).Select(e => e["key1"]) .Where(e => e["key2"] != null).Select(e => e["key2"])
有没有办法用一个Where
语句过滤嵌套键?
您可以使用JToken.SelectTokens()
在LINQ to JSON对象上运行嵌套查询:
var valueQuery = globalEventStream .Select(e => JObject.Parse(e.EventArgs.Data)) .Where(o => o.SelectTokens("Key1.key2").Any());
样品小提琴 。
JSONPath的规范在这里,并支持以下查询语法:
XPath JSONPath Description / $ the root object/element . @ the current object/element / . or [] child operator .. n/a parent operator // .. recursive descent. JSONPath borrows this syntax from E4X. * * wildcard. All objects/elements regardless their names. @ n/a attribute access. JSON structures don't have attributes. [] [] subscript operator. XPath uses it to iterate over element collections and for predicates. In Javascript and JSON it is the native array operator. | [,] Union operator in XPath results in a combination of node sets. JSONPath allows alternate names or array indices as a set. n/a [start:end:step] array slice operator borrowed from ES4. [] ?() applies a filter (script) expression. n/a () script expression, using the underlying script engine. () n/a grouping in Xpath
例如,对于以下JSON:
{ "Key1" : [{"NoKey2":"value"}, {"key2":"value"}], "key3" : "other values" }
您可以使用通配符运算符*
来测试数组中是否存在具有"key2"
属性的任何项,如下所示:
var valueQuery = globalEventStream .Select(e => JObject.Parse(e.EventArgs.Data)) .Where(o => o.SelectTokens("Key1[*].key2").Any());
这里Enumerable.Any()
测试以查看SelectTokens()
查询是否发现多于零的结果 – 即, "Key1"
数组中是否至少有一个条目具有"key2"
属性。 它比执行Enumerable.Count()
更有效,因为它会在返回一个项目后立即停止评估。