.NET 4.5中如何将GraphQL字符串解析为对象？

一、使用兼容的GraphQL解析库 #

.NET Framework 4.5可选用GraphQL.NET 2.4.0版本（该版本明确支持.NET Framework 4.5），借助它的AST（抽象语法树）解析能力完成转换：

1. 安装对应NuGet包：

   Install-Package GraphQL -Version 2.4.0
   

2. 解析GraphQL字符串并映射到自定义类的示例代码：

   using GraphQL;
   using GraphQL.Language.AST;
   using Newtonsoft.Json.Linq;
   
   public static class GraphQLParserHelper
   {
       public static GraphQL ParseToCustomGraphQL(string graphqlStr)
       {
           var document = Parser.Parse(graphqlStr);
           var graphQL = new GraphQL { Query = new List<Field>() };
   
           var operation = document.Operations.FirstOrDefault() as Operation;
           if (operation != null)
           {
               foreach (var selection in operation.Selections)
               {
                   if (selection is Field fieldAst)
                   {
                       graphQL.Query.Add(MapFieldAstToCustomField(fieldAst));
                   }
               }
           }
   
           return graphQL;
       }
   
       private static Field MapFieldAstToCustomField(GraphQL.Language.AST.Field fieldAst)
       {
           var customField = new Field
           {
               Name = fieldAst.Name,
               Alias = fieldAst.Alias?.Name ?? "",
               Fields = new List<Field>()
           };
   
           if (fieldAst.Arguments != null && fieldAst.Arguments.Any())
           {
               var argsObj = new JObject();
               foreach (var arg in fieldAst.Arguments)
               {
                   argsObj[arg.Name] = GetArgumentValue(arg.Value);
               }
               customField.Attributes = argsObj;
           }
   
           foreach (var selection in fieldAst.Selections)
           {
               if (selection is Field nestedFieldAst)
               {
                   customField.Fields.Add(MapFieldAstToCustomField(nestedFieldAst));
               }
           }
   
           return customField;
       }
   
       private static JToken GetArgumentValue(IValue value)
       {
           if (value is StringValue strVal)
               return JToken.FromObject(strVal.Value);
           if (value is IntValue intVal)
               return JToken.FromObject(intVal.Value);
           if (value is BooleanValue boolVal)
               return JToken.FromObject(boolVal.Value);
           return JValue.CreateNull();
       }
   }
   
   // 你的自定义类
   public class GraphQL
   {
       public List<Field> Query { get; set; }
   }
   
   public class Field
   {
       public string Name { get; set; }
       public string Alias { get; set; } = "";
       public JObject Attributes { get; set; }
       public List<Field> Fields { get; set; }
   }
   

二、纯自定义解析（无第三方库） #

如果不想依赖第三方库，可通过正则配合递归实现基础解析（仅适合简单场景，复杂语法如片段、变量等需额外扩展）：

using System.Text.RegularExpressions;
using Newtonsoft.Json.Linq;

public static class CustomGraphQLParser
{
    private static readonly Regex FieldRegex = new Regex(@"([\w]+)(?:\:([\w]+))?\s*(?:\((.*?)\))?\s*(?:\{(.*?)\})?", RegexOptions.Singleline | RegexOptions.Compiled);

    public static GraphQL Parse(string graphqlStr)
    {
        var cleanStr = Regex.Replace(graphqlStr, @"\s+", " ").Trim();
        var match = FieldRegex.Match(cleanStr);
        var graphQL = new GraphQL { Query = new List<Field>() };

        while (match.Success)
        {
            var field = new Field
            {
                Alias = match.Groups[1].Value,
                Name = match.Groups[2].Success ? match.Groups[2].Value : match.Groups[1].Value,
                Fields = new List<Field>()
            };

            var argsStr = match.Groups[3].Value;
            if (!string.IsNullOrEmpty(argsStr))
            {
                var argsObj = new JObject();
                var args = argsStr.Split(',');
                foreach (var arg in args)
                {
                    var parts = arg.Split(':', StringSplitOptions.RemoveEmptyEntries);
                    if (parts.Length == 2)
                    {
                        argsObj[parts[0].Trim()] = parts[1].Trim().Trim('"');
                    }
                }
                field.Attributes = argsObj;
            }

            var nestedFieldsStr = match.Groups[4].Value;
            if (!string.IsNullOrEmpty(nestedFieldsStr))
            {
                var nestedGraphQL = Parse($"{{{nestedFieldsStr}}}");
                field.Fields.AddRange(nestedGraphQL.Query);
            }

            graphQL.Query.Add(field);
            match = match.NextMatch();
        }

        return graphQL;
    }
}

注意：纯自定义解析仅支持基础的字段、别名、参数和嵌套结构，对于GraphQL的复杂语法（如变量、片段、指令等）处理能力有限，建议优先使用第一种方案。

内容的提问来源于stack exchange，提问作者Divyesh Chaudhari