Newtonsoft.Json.Linq.JObject.GetValue("[key]").ToObject<DataTable>相关问题

2019/12/02 10:46
阅读数 212

 

我们用Newtonsoft.Json.Linq.JObject.GetValue("[key]").ToObject<DataTable>方法把一个JObject对象中的某个节点转换成DataTable格式的数据很方便。一直这样用也没出什么问题。但是最近发现在某些情况下,这种数据转换其实是有一定的问题甚至报错。场景如下:

1. 当数据源类似如下时。当把Data节点的数据转换成DataTable格式时,会默认abc字段为整型,导致在对第二条数据做转换时,50.11会丢失精度,变成整型50

"{\"Data\":[{\"abc\":50},{\"abc\":50.01}]}"

2. 当数据源类似如下时。就会导致第二条数据在转化成INT类型时出错。

"{\"Data\":[{\"abc\":50},{\"abc\":\"xyz\"}]}"

 

这个就需要用到ToObject的JsonSerializer参数了。通过重写serializer方法,来具体指定某一列的数据类型,从而达到效果。

public class CustomDataTableConverter : DataTableConverter
{
    private static void CreateRow(JsonReader reader, DataTable dt)
    {
        DataRow row = dt.NewRow();
        reader.Read();

        while(reader.TokenType == JsonToken.PropertyName)
        {
            string columnName = (string)reader.Value;
            reader.Read();
            DataColumn column = dt.Columns[columnName];
            if(column == null)
            {
                Type columnDataType = GetColumnDataType(reader);
                column = new DataColumn(columnName, columnDataType);
                dt.Columns.Add(column);
            }
            if(column.DataType == typeof(DataTable))
            {
                 if(reader.TokenType == JsonToken.StartArray)
                 {
                     reader.Read();
                 }
                 DataTable table = new DataTable();
                 while(reader.TokenType != JsonToken.EndArray)
                 {
                     CreateRow(reader, table);
                     reader.Read();
                 }
                 row[columnName] = table;
            }
            else if(column.DataType.IsArray && (column.DataType != typeof(byte[])))
            {
                if(reader.TokenType == JsonToken.StartArray)
                 {
                     reader.Read();
                 }
                 List<object> list = new List<object>();
                 while(reader.TokenType != JsonToken.EndArray)
                 {
                     list.Add(reader.Value);
                     reader.Read();
                 }
                 Array destinationArray = Array.CreateInstance(column.DataType.GetElementType(), list.Count);
                 Array.Copy(list.ToArray(), destinationArray, list.Count);
                 row[columnName] = destinationArray;
            }
            else
            {
                object val = DBNull.Value;
                if(reader.Value != null)
                {
                    if(column.DataType == typeof(string))
                    {
                         val = reader.Value.ToString();
                    }
                    else
                    {
                        if(string.IsNullOrEmpty(reader.Value.ToString()))
                        {
                            val = DBNull.Value;
                        }
                        else
                        {
                            val = Convert.ChangeType(reader.Value, column.DataType);
                        }
                    }
                    row[columnName] = val;
                }
                reader.Read();
            }    
            row.EndEdit();
            dt.Rows.Add(row);
        }
    }  

    private static Type GetColumnDataType(JsonReader reader)
    {
        JsonToken tokenType = reader.TokenType;
        switch(tokenType)
        {
            case JsonToken.StartArray:
                reader.Read();
                if(reader.TokenType != JsonToken.StartObject)
                {
                     return GetColumnDataType(reader).MakeArrayType();
                }
                return typeof(DataTable);
            //这个地方需要对数值类型做特殊处理。如果能确认是数值列,那么可以用double类型替代,防止精度丢失。如果是字符串类型列,那么使用string类型,防止数据转化出错     
            case JsonToken.Integer:
                return typeof(double);
            case JsonToken.Float:
            case JsonToken.String:
            case JsonToken.Boolean:
            case JsonToken.Date:
            case JsonToken.Bytes:
                return reader.ValueType;
            case JsonToken.Null:
            case JsonToken.Undefined:
                return typeof(string);
        }
        throw new JsonException($"Unexpected JSON token while reading DataTable: {tokenType}");
    }

    private static void MakeTableSchema(string schema, DataTable dt)
    {
        if(!string.IsNullOrEmpty(schema) && dt != null)
        {
            string[] colinfos = schema.Trim(',').Split(',');
            foreach(string colinfo in colinfos)
            {
                string[] info = colinfo.split('|');
                if(!dt.Columns.Contains(info[0]))
                {
                    dt.Columns.Add(info[0], Type.GetType("System." + info[i]));
                } 
            }
        }
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        DataTable dt = existingValue as DataTable;
        if(dt == null)
        {
            dt = (objectType == typeof(DataTable)) ? new DataTable() : ((DataTable)Activator.CreateInstance(objectType));
        }
        if(reader.TokenType == JsonToken.PropertyName)
        {
            dt.TableName = (string)reader.Value;
            reader.Read();
        }
        if(reader.TokenType == JsonToken.StartObject)
        {
            reader.Read();
            while(reader.TokenType == JsonToken.PropertyName)
            {
                if((string)reader.Value == "SCHEMA")
                {
                    reader.Read();
                    MakeTableSchema((string)reader.Value, dt);
                    reader.Read();
                }
                if((string)reader.Value == "TABLENAME")
                {
                    reader.Read();
                    dt.TableName = (string)reader.Value;
                    reader.Read();
                }
                else if((string)reader.Value == "DATA")
                {
                    reader.Read();
                    if(reader.TokenType == JsonToken.StartArray)
                    {
                        reader.Read();
                    }
                    while(reader.TokenType != JsonToken.EndArray)
                    {
                         CreateRow(reader, dt);
                         reader.Read();
                     }
                }
            }
            reader.Read();
        }
        else if(reader.TokenType == JsonToken.StartArray)
        {
            reader.Read();
            while(reader.TokenType != JsonToken.EndArray)
            {
                Create(reader, dt);
                reader.Read();
            }
        }
        return dt;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        DataTable table = (DataTable)value;
        DefaultContractResolver contractResolver = serializer.ContractResolver as DefaultContractResolver;
        StringBuilder sb = new StringBuilder();
        foreach(DataColumns column in table.Columns)
        {
            sb.Append(column.ColumnName + "|" + column.DataType.Name + ",");
        }
        writer.WriteStartObject();
        writer.WritePropertyName("SCHEMA");
        serializer.Serializer(writer, sb.ToString());
        writer.WritePropertyName("TABLENAME");
        serializer.Serialize(writer, table.TableName);
        writer.WritePropertyName("DATA");
        writer.WriteStartArray();
        foreach(DataRow row in table.Rows)
        {
            writer.WriteStartObject();
            foreach(DataColumn column in row.Table.Columns)
            {
                 if((serializer.NullValueHandling != NullValueHanding.Ignore) || ((row[column] != null) && (row[column] != DBNull.Value)))
                 {
                     writer.WritePropertyName((contractResolver != null) ? contractResolver.GetResolvedPropertyName(column.ColumnName) : column.ColumnName);
                     serializer.Serialize(writer, row[column]);
                 }
            }
            writer.WriteEndObject();
        }
        writer.WriteEndArray();
        writer.WriteEndObject();
    }
}

 

调用方法

JsonSerializer serializer = new JsonSerializer();
serializer.Converts.Add(new CustomDataTableConverter());
JObject.GetValue("[Key]").ToObject<DataTable>(serializer);

 

这样就能相对正确地把数据转成DataTable。

 

展开阅读全文
打赏
0
0 收藏
分享
加载中
更多评论
打赏
0 评论
0 收藏
0
分享
返回顶部
顶部