嵌套LINQ to XML检索报错：输入字符串格式不正确问题排查

原始XML结构 #

<Tournament TeamPlayers="1">
    <Teams>
        <Team>
            <TeamID></TeamID>
            <Name></Name>
            <Status></Status>
            <Memo></Memo>
            <ByeRounds></ByeRounds>
            <Players>
                <Player Seat="A">
                    <MemberNo></MemberNo>
                    <MemberName></MemberName>
                    <PlayerFirstName></PlayerFirstName>
                    <PlayerLastName></PlayerLastName>
                </Player>
            </Players>
        </Team>
    </Teams>
    <Staff>
        <Player>
            <MembershipNo></MembershipNo>
            <PlayerFirstName></PlayerFirstName>
            <PlayerLastName></PlayerLastName>
            <MembershipName></MembershipName>
            <Position></Position>
        </Player>
    </Staff>
    
    <Penalties>
        <Penalty>
            <Judge></Judge>
            <Player></Player>
            <InfractionType></InfractionType>
            <PenaltyType></PenaltyType>
            <Notes></Notes>
        </Penalty>
    </Penalties>
</Tournament>

问题场景与错误代码 #

需求是遍历<Teams>、<Staff>、<Penalty>节点并存入列表，但编写的VB.NET代码无法正确嵌套访问<Players>元素，运行时提示**"Input string was not in a correct format"**错误，原始代码如下：

Dim TeamsNodes = xDoc.Descendants("Teams")

    lstOutputTeams = team.Descendants("Team").[Select](Function(t) New TournamentTeam With {
                                          .intTeamID = t.Element("TeamID"),
                                          .intByeRounds = t.Element("ByeRounds"),
                                          .strTeamName = t.Element("Name"),
                                          .strMemo = t.Element("Memo"),
                                          .intStatus = t.Element("Status"),
                                          .tpPlayerA = (From p In team.Descendants("Players") Select New PlayerInfo With {
                                                    .strMembershipNo = p.Element("MemberNo").Value,
                                                    .strPlayerFirstName = p.Element("PlayerFirstName").Value,
                                                    .strPlayerLastName = p.Element("PlayerLastName").Value,
                                                    .strMembershipName = p.Element("MemberName")})
                                        }).ToList()
Next

lstFinalOutput.Add(lstOutputTeams)

错误原因分析 #

1. 数值类型转换错误：intTeamID、intByeRounds、intStatus是数值类型，但代码直接将XElement对象赋值给它们，且XML中这些元素可能为空，直接取Value转数值时会因空字符串抛出格式错误。
2. Players节点层级访问错误：
   • 应该从当前Team节点t下查找Players，而非外层的team变量；
   • MemberNo等字段属于<Player>节点，而非<Players>节点，原代码层级定位错误。
3. 集合类型不匹配：tpPlayerA应为单个PlayerInfo对象，但原代码用Select返回了IEnumerable(Of PlayerInfo)，类型不匹配。
4. 空值未处理：XML元素可能为空，直接访问.Value会引发空引用异常或格式转换错误。

修正后的代码 #

' 假设xDoc是已加载的XDocument对象
Dim TeamsNodes = xDoc.Descendants("Teams")

' 遍历每个Teams节点下的Team
For Each teamNode In TeamsNodes
    lstOutputTeams = teamNode.Descendants("Team").Select(Function(t) New TournamentTeam With {
        ' 处理数值类型的空值转换，空值时设默认值0
        .intTeamID = If(String.IsNullOrEmpty(t.Element("TeamID")?.Value), 0, Integer.Parse(t.Element("TeamID").Value)),
        .intByeRounds = If(String.IsNullOrEmpty(t.Element("ByeRounds")?.Value), 0, Integer.Parse(t.Element("ByeRounds").Value)),
        .intStatus = If(String.IsNullOrEmpty(t.Element("Status")?.Value), 0, Integer.Parse(t.Element("Status").Value)),
        ' 字符串类型处理空元素，转为空字符串
        .strTeamName = t.Element("Name")?.Value ?? "",
        .strMemo = t.Element("Memo")?.Value ?? "",
        ' 定位当前Team下Seat="A"的Player，转为单个PlayerInfo对象
        .tpPlayerA = t.Descendants("Player").FirstOrDefault(Function(p) p.Attribute("Seat")?.Value = "A")?.
            Let(playerNode = New PlayerInfo With {
                .strMembershipNo = playerNode.Element("MemberNo")?.Value ?? "",
                .strPlayerFirstName = playerNode.Element("PlayerFirstName")?.Value ?? "",
                .strPlayerLastName = playerNode.Element("PlayerLastName")?.Value ?? "",
                .strMembershipName = playerNode.Element("MemberName")?.Value ?? ""
            })
    }).ToList()
    lstFinalOutput.Add(lstOutputTeams)
Next

关键修正点说明 #

• 数值类型字段增加空值判断，用If和Integer.Parse安全转换，空值时设默认值；
• 字符串字段用空合并运算符??处理空元素，避免空引用；
• 调整Players节点的查找层级，从当前Team节点t下找Player，并通过FirstOrDefault获取单个匹配Seat="A"的对象；
• 用?.空传播运算符避免空元素访问时的异常。

内容的提问来源于stack exchange，提问作者Paul Williams