如何在JSON中为空的DataTable包含列元数据

如何在JSON中为空的DataTable包含列元数据

该

DataTableConverter

附带Json.Net不输出列的元数据，即使你设置

TypeNameHandling

到

All

。但是，没有什么可以阻止您制作自己的自定义转换器来执行此 *** 作，而是使用该自定义转换器。以下是我根据您的需求拼凑而成的一种：

class CustomDataTableConverter : JsonConverter{    public override bool CanConvert(Type objectType)    {        return (objectType == typeof(DataTable));    }    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)    {        DataTable dt = (DataTable)value;        JObject metaDataObj = new JObject();        foreach (DataColumn col in dt.Columns)        { metaDataObj.Add(col.ColumnName, col.DataType.AssemblyQualifiedName);        }        JArray rowsArray = new JArray();        rowsArray.Add(metaDataObj);        foreach (DataRow row in dt.Rows)        { JObject rowDataObj = new JObject(); foreach (DataColumn col in dt.Columns) {     rowDataObj.Add(col.ColumnName, JToken.FromObject(row[col])); } rowsArray.Add(rowDataObj);        }        rowsArray.WriteTo(writer);    }    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)    {        JArray rowsArray = JArray.Load(reader);        JObject metaDataObj = (JObject)rowsArray.First();        DataTable dt = new DataTable();        foreach (JProperty prop in metaDataObj.Properties())        { dt.Columns.Add(prop.Name, Type.GetType((string)prop.Value, throwOnError: true));        }        foreach (JObject rowDataObj in rowsArray.Skip(1))        { DataRow row = dt.NewRow(); foreach (DataColumn col in dt.Columns) {     if (rowDataObj[col.ColumnName].Type != JTokenType.Null)//Skip if the Value is Null/Missing, especially for a non-nullable type.         row[col] = rowDataObj[col.ColumnName].ToObject(col.DataType); } dt.Rows.Add(row);        }        return dt;    }}

这是一个演示。请注意，序列化表时，列类型被写为JSON中数组的第一行。反序列化时，即使没有其他行，此元数据也将用于使用正确的列类型和名称重建表。（您可以通过在顶部将行数据添加到表中的两行注释掉来验证这一点。）

class Program{    static void Main(string[] args)    {        DataTable dt = new DataTable();        dt.Columns.Add("PackageID", typeof(int));        dt.Columns.Add("Amount", typeof(int));        dt.Columns.Add("Auto_sync", typeof(bool));        dt.Columns.Add("Color", typeof(string));        // Comment out these two lines to see the table with no data.        // Test with a null Value for a Non-Nullable DataType.        dt.Rows.Add(new object[] { 226,  null, true, "BLUE" });        dt.Rows.Add(new object[] { 500, 15000, true, "PEACH" });        Foo foo = new Foo        { BrokerID = "998", AccountID = "1313", Packages = dt        };        JsonSerializerSettings settings = new JsonSerializerSettings();        settings.Converters.Add(new CustomDataTableConverter());        settings.Formatting = Formatting.Indented;        string json = JsonConvert.SerializeObject(foo, settings);        Console.WriteLine(json);        Console.WriteLine();        Foo foo2 = JsonConvert.DeserializeObject<Foo>(json, settings);        Console.WriteLine("BrokerID: " + foo2.BrokerID);        Console.WriteLine("AccountID: " + foo2.AccountID);        Console.WriteLine("Packages table:");        Console.WriteLine("  " + string.Join(", ",  foo2.Packages.Columns     .Cast<DataColumn>()     .Select(c => c.ColumnName + " (" + c.DataType.Name + ")")));        foreach (DataRow row in foo2.Packages.Rows)        { Console.WriteLine("  " + string.Join(", ", row.ItemArray     .Select(v => v != null ? v.ToString() : "(null)")));        }    }}class Foo{    public string BrokerID { get; set; }    public string AccountID { get; set; }    public DataTable Packages { get; set; }}

输出：

{  "BrokerID": "998",  "AccountID": "1313",  "Packages": [    {      "PackageID": "System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089",      "Amount": "System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089",      "Auto_sync": "System.Boolean, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089",      "Color": "System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"    },    {      "PackageID": 226,      "Amount": null,      "Auto_sync": true,      "Color": "BLUE"    },    {      "PackageID": 500,      "Amount": 15000,      "Auto_sync": true,      "Color": "PEACH"    }  ]}BrokerID: 998AccountID: 1313Packages table:  PackageID (Int32), Amount (Int32), Auto_sync (Boolean), Color (String)  226, , True, BLUE  500, 15000, True, PEACH

小提琴：https :
//dotnetfiddle.net/GGrn9z