JSON.Net - 从多态 json 字符串中检索另一个数据答案

【问题标题】：JSON.Net - Another data retrieval from a polymorphic json stringJSON.Net - 从多态 json 字符串中检索另一个数据
【发布时间】：2016-10-20 13:59:30
【问题描述】：

这是我的 JSON 字符串的样子：

{
    "?xml" : {
        "@version" : "1.0",
        "@encoding" : "UTF-8"
    },
    "DataFeed" : {
        "@FeedName" : "content",
        "now" : "2016-10-17T14:11:38.00",
        "Content" : [{
                "ContentData" : {
                    "@statusType" : "Published",
                    "@isReleased" : "Yes",
                    "@docId" : "21756",
                    "ProductStatus" : {
                        "@productCategory" : "Issuer",
                        "@focus" : "Issuer",
                        "Symbol" : {
                            "@PrimarySymbol" : "GOOGL",
                            "@SecondarySymbol" : "Google",
                            "@BmId" : "1790"
                        }
                    },
                    "ContentVersion" : {
                        "@versionId" : "1",
                        "@lastVersion" : "true",
                        "@lastPublished" : "true",
                        "Url" : [{
                                "@type" : "XML",
                                "@size" : "146410",
                                "#cdata-section" : "https://aaa.yyy.com/docs/xml/708893eb-1fd9-4278-8b0e-e7e0738d8105.xml"
                            }, {
                                "@type" : "HTML",
                                "@size" : "46105",
                                "#cdata-section" : "https://aaa.yyy.com/docs/html/708893eb-1fd9-4278-8b0e-e7e0738d8105.html"
                            }, {
                                "@type" : "PDF",
                                "@size" : "1274885",
                                "#cdata-section" : "https://aaa.yyy.com/docs/pdf/708893eb-1fd9-4278-8b0e-e7e0738d8105.pdf"
                            }, {
                                "@type" : "ALTERNATE PDF",
                                "@size" : "60960",
                                "#cdata-section" : "https://aaa.yyy.com/docs/shortPdf/708893eb-1fd9-4278-8b0e-e7e0738d8105.pdf"
                            }
                        ]
                    }
                }
            }, {
                "ContentData" : {
                    "@statusType" : "Published",
                    "@isReleased" : "Yes",
                    "@docId" : "22457",
                    "ProductStatus" : {
                        "@productCategory" : "Issuer",
                        "@focus" : "Issuer",
                        "Symbol" : {
                            "@PrimarySymbol" : "AAPL",
                            "@SecondarySymbol" : "Apple",
                            "@BmId" : "1121"
                        }
                    },
                    "ContentVersion" : [{
                            "@versionId" : "1",
                            "@lastVersion" : "false",
                            "@lastPublished" : "false",
                            "Url" : [{
                                    "@type" : "XML",
                                    "#cdata-section" : "https://aaa.yyy.com/docs/version/708893eb-1fd9-4278-8b0e-e7e0738d8105.1476742297.xml"
                                }, {
                                    "@type" : "HTML",
                                    "#cdata-section" : "https://aaa.yyy.com/docs/version/708893eb-1fd9-4278-8b0e-e7e0738d8105.1476742297.html"
                                }, {
                                    "@type" : "PDF",
                                    "#cdata-section" : "https://aaa.yyy.com/docs/version/708893eb-1fd9-4278-8b0e-e7e0738d8105.1476742297.pdf"
                                }, {
                                    "@type" : "ALTERNATE PDF",
                                    "#cdata-section" : "https://aaa.yyy.com/docs/version/708893eb-1fd9-4278-8b0e-e7e0738d8105.1476742297_short.pdf"
                                }
                            ]
                        }, {
                            "@versionId" : "2",
                            "@lastVersion" : "true",
                            "@lastPublished" : "true",
                            "Url" : [{
                                    "@type" : "XML",
                                    "@size" : "174520",
                                    "#cdata-section" : "https://aaa.yyy.com/docs/xml/708893eb-1fd9-4278-8b0e-e7e0738d8105.xml"
                                }, {
                                    "@type" : "HTML",
                                    "@size" : "46105",
                                    "#cdata-section" : "https://aaa.yyy.com/docs/html/708893eb-1fd9-4278-8b0e-e7e0738d8105.html"
                                }, {
                                    "@type" : "PDF",
                                    "@size" : "1270150",
                                    "#cdata-section" : "https://aaa.yyy.com/docs/pdf/708893eb-1fd9-4278-8b0e-e7e0738d8105.pdf"
                                }, {
                                    "@type" : "ALTERNATE PDF",
                                    "@size" : "60960",
                                    "#cdata-section" : "https://aaa.yyy.com/docs/version/708893eb-1fd9-4278-8b0e-e7e0738d8105.1577742297_short.pdf"
                                }
                            ]
                        }
                    ]
                }
            }, {
                "ContentData" : {
                    "@statusType" : "Published",
                    "@isReleased" : "Yes",
                    "@docId" : "22501",
                    "ProductStatus" : {
                        "@productCategory" : "Issuer",
                        "@focus" : "Issuer",
                        "Symbol" : [{
                                "@PrimarySymbol" : "AAA",
                                "@SecondarySymbol" : "Some name 1",
                                "@BmId" : "561"
                            }, {
                                "@PrimarySymbol" : "ABC",
                                "@SecondarySymbol" : "Some Name 2",
                                "@BmId" : "29"
                            }, {
                                "@PrimarySymbol" : "BBB",
                                "@SecondarySymbol" : "Some Name 3",
                                "@BmId" : "36"
                            }, {
                                "@PrimarySymbol" : "CCC",
                                "@SecondarySymbol" : "Some Name 4",
                                "@BmId" : "624"
                            }
                        ]
                    },
                    "ContentVersion" : {
                        "@versionId" : "1",
                        "@lastVersion" : "true",
                        "@lastPublished" : "true",
                        "Url" : [{
                                "@type" : "XML",
                                "@size" : "2706269",
                                "#cdata-section" : "https://aaa.yyy.com/docs/xml/1c420081-0ce5-4959-91d3-848bbbccd3e3.xml"
                            }, {
                                "@type" : "HTML",
                                "@size" : "32445",
                                "#cdata-section" : "https://aaa.yyy.com/docs/html/1c420081-0ce5-4959-91d3-848bbbccd3e3.html"
                            }, {
                                "@type" : "PDF",
                                "@size" : "887608",
                                "#cdata-section" : "https://aaa.yyy.com/docs/pdf/1c420081-0ce5-4959-91d3-848bbbccd3e3.pdf"
                            }, {
                                "@type" : "ALTERNATE PDF",
                                "@size" : "34366",
                                "#cdata-section" : "https://aaa.yyy.com/docs/shortPdf/1c420081-0ce5-4959-91d3-848bbbccd3e3.pdf"
                            }
                        ]
                    }
                }
            }
        ]
    }
}

我正在关注LINQ to Json data retrieval from polymorphic json 中的代码示例。我想选择以下内容，但前提是Symbol 部分中只有一个发行者并且最新版本的 PDF url：

@docId
@PrimarySymbol
@BmId
#cdata-section（但仅适用于最新版本的 PDF）

我的查询如下所示：

from content in jsonFeed.SelectTokens("DataFeed.Content").SelectMany(i => i.ObjectsOrSelf())
let issuer = content
        .SelectToken("ContentData.ProductStatus.@productCategory")
        .SingleOrMultiple()
        .Select(t => (string)t)
        .ToArray()
where issuer.FirstOrDefault().Equals("Issuer")
select new 
{
    DocID = (string)content.SelectToken("ContentData.@docId"),
    Symbol = (string)content.SelectToken("ContentData.ProductStatus.Symbol.@PrimarySymbol"),
    BMId = (int)content.SelectToken("ContentData.ProductStatus.Symbol.@BmId"),
    PDFUrl = (string)content.SelectToken("ContentData.ContentVersion.Url[3].#cdata-section")
}).ToList();

目前，我可以成功获取 Google 的所有字段，但无法获取 Apple 的 PDFUrl（因为我不知道如何获取最新版本）。另外，我怎样才能完成我的 Where 子句，以便它只选择带有 1 个符号的文档？所以，最后，我的清单将如下图所示：

【问题讨论】：

您想要"@type" : "PDF" URL 还是"@type" : "ALTERNATE PDF" URL？因为您目前正在获取索引 3 处的那个，这是备用 PDF 网址。
就"@type": "PDF".

标签： c# linq c#-4.0 json.net linq-to-json

【解决方案1】：

您可以结合let 和where 来计算和过滤中间结果。

以下查询使用了这种技术，并且还查询了 @type 等于 "PDF" 的 URL，而不是将其硬编码为索引 3（顺便说一下，它实际上位于索引 2）：

string pdfUrlType = "PDF";
var query =
    (from content in jsonFeed.SelectTokens("DataFeed.Content").SelectMany(i => i.ObjectsOrSelf())
     let issuer = content
             .SelectToken("ContentData.ProductStatus.@productCategory")
             .SingleOrMultiple()
             .Select(t => (string)t)
             .ToArray()
     where issuer.FirstOrDefault().Equals("Issuer")
     // Get the @PrimarySymbol where there is exactly one, or null otherwise.
     let symbol = (string)content.SelectToken("ContentData.ProductStatus.Symbol.@PrimarySymbol")
     // Skip content without a single primary symbol
     where symbol != null
     // Get the last ContentVersion record in the JSON document.
     let lastContentVersion = content
        .SelectToken("ContentData.ContentVersion")
        .SingleOrMultiple()
        .Where(v => (bool?)v.SelectToken("@lastVersion") == true)
        .LastOrDefault()
     // Skip content with no ContentVersion
     where lastContentVersion != null
     // Get the PDF Url record
     let pdfUrl = lastContentVersion.SelectToken("Url")
        .SingleOrMultiple()
        .Where(u => (string)u.SelectToken("@type") == pdfUrlType)
        .FirstOrDefault()
     // Skip content with no PDF Url record
     where pdfUrl != null
     select new
     {
         DocID = (string)content.SelectToken("ContentData.@docId"),
         Symbol = symbol,
         BMId = (int?)content.SelectToken("ContentData.ProductStatus.Symbol.@BmId"),
         PDFUrl = (string)pdfUrl.SelectToken("#cdata-section")
     }).ToList();

如果您确实想要替代 PDF 网址，请设置

string pdfUrlType = "ALTERNATE PDF";

示例fiddle。

如果您确定每个"Content" 记录中的最新版本ContentVersion（"@lastVersion" 等于"true" 的记录）按文档顺序保证是最后一个，则可以简化查询如下：

     let lastContentVersion = content
        .SelectToken("ContentData.ContentVersion")
        .SingleOrMultiple()
        .LastOrDefault()

【讨论】：