从 SqlDataReader 创建 JSON 字符串

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我想通了。 Check out my answer below.

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我正在尝试创建一个 JSON 字符串来表示数据库表中的一行以在 HTTP 响应中返回。似乎Json.NET 将是一个很好的工具。但是，我不确定如何构建 JSON 字符串而我正在从数据库中读取。

问题被讨厌的cmets标记/******** ********/

// connect to DB
theSqlConnection.Open(); // open the connection

SqlDataReader reader = sqlCommand.ExecuteReader();
if (reader.HasRows) {

    while(reader.Read()) {

        StringBuilder sb = new StringBuilder();
        StringWriter sw = new StringWriter(sb);

        using (JsonWriter jsonWriter = new JsonTextWriter(sw)) {

            // read columns from the current row and build this JsonWriter
            jsonWriter.WriteStartObject();
            jsonWriter.WritePropertyName("FirstName");

            // I need to read the value from the database
/******** I can't just say reader[i] to get the ith column. How would I loop here to get all columns? ********/
            jsonWriter.WriteValue(... ? ...);
            jsonWriter.WritePropertyName("LastName");
            jsonWriter.WriteValue(... ? ...);
            jsonWriter.WritePropertyName("Email");
            jsonWriter.WriteValue(... ? ...);

            // etc...
            jsonWriter.WriteEndObject();
        }
    }
}

问题是我不知道如何从SqlReader 的行中读取每一列，以便我可以调用WriteValue 并为其提供正确的信息并将其附加到正确的列名。所以如果一行看起来像这样......

| FirstName | LastName | Email |

...我将如何为每个这样的行创建一个JsonWriter，以便它包含该行的所有列名和每列中的相应值，然后使用该JsonWriter 来构建一个准备好的 JSON 字符串用于通过 HTTP 响应返回？

如果我需要澄清任何事情，请告诉我。

Answer 1

我的版本：

这不使用 DataSchema，还将结果包装在一个数组中，而不是每行使用一个写入器。

SqlDataReader rdr = cmd.ExecuteReader();

StringBuilder sb = new StringBuilder();
StringWriter sw = new StringWriter(sb);    

using (JsonWriter jsonWriter = new JsonTextWriter(sw)) 
{    
    jsonWriter.WriteStartArray();

    while (rdr.Read())
    {
        jsonWriter.WriteStartObject();

        int fields = rdr.FieldCount;

        for (int i = 0; i < fields; i++)
        { 
            jsonWriter.WritePropertyName(rdr.GetName(i));
            jsonWriter.WriteValue(rdr[i]);
        }

        jsonWriter.WriteEndObject();
    }

    jsonWriter.WriteEndArray();
}

Answer 2

针对具体示例进行了编辑：

theSqlConnection.Open();

SqlDataReader reader = sqlCommand.ExecuteReader();
DataTable schemaTable = reader.GetSchemaTable();

foreach (DataRow row in schemaTable.Rows)
{
    StringBuilder sb = new StringBuilder();
    StringWriter sw = new StringWriter(sb);

    using (JsonWriter jsonWriter = new JsonTextWriter(sw)) 
    {    
        jsonWriter.WriteStartObject();

        foreach (DataColumn column in schemaTable.Columns)
        {
            jsonWriter.WritePropertyName(column.ColumnName);
            jsonWriter.WriteValue(row[column]);
        }

        jsonWriter.WriteEndObject();
    }
}

theSqlConnection.Close();

Answer 3

知道了！这是 C#...

// ... SQL connection and command set up, only querying 1 row from the table
StringBuilder sb = new StringBuilder();
StringWriter sw = new StringWriter(sb);
JsonWriter jsonWriter = new JsonTextWriter(sw);

try {

    theSqlConnection.Open(); // open the connection

    // read the row from the table
    SqlDataReader reader = sqlCommand.ExecuteReader();
    reader.Read();

    int fieldcount = reader.FieldCount; // count how many columns are in the row
    object[] values = new object[fieldcount]; // storage for column values
    reader.GetValues(values); // extract the values in each column

    jsonWriter.WriteStartObject();
    for (int index = 0; index < fieldcount; index++) { // iterate through all columns

        jsonWriter.WritePropertyName(reader.GetName(index)); // column name
        jsonWriter.WriteValue(values[index]); // value in column

    }
    jsonWriter.WriteEndObject();

    reader.Close();

} catch (SqlException sqlException) { // exception
    context.Response.ContentType = "text/plain";
    context.Response.Write("Connection Exception: ");
    context.Response.Write(sqlException.ToString() + "\n");
} finally {
    theSqlConnection.Close(); // close the connection
}
// END of method
// the above method returns sb and another uses it to return as HTTP Response...
StringBuilder theTicket = getInfo(context, ticketID);
context.Response.ContentType = "application/json";
context.Response.Write(theTicket);

...所以StringBuilder sb 变量是代表我想要查询的行的 JSON 对象。这里是 JavaScript...

$.ajax({
    type: 'GET',
    url: 'Preview.ashx',
    data: 'ticketID=' + ticketID,
    dataType: "json",
    success: function (data) {

        // data is the JSON object the server spits out
        // do stuff with the data
    }
});

感谢Scott 的回答，他的回答启发了我找到解决方案。

Hristo

Answer 4

我做了以下方法，它将任何 DataReader 转换为 JSON，但仅用于单深度序列化：

你应该将 reader 和列名作为字符串数组传递，例如：

String [] columns = {"CustomerID", "CustomerName", "CustomerDOB"};

然后调用方法

public static String json_encode(IDataReader reader, String[] columns)
    {
        int length = columns.Length;

        String res = "{";

        while (reader.Read())
        {
            res += "{";

            for (int i = 0; i < length; i++)
            {
                res += "\"" + columns[i] + "\":\"" + reader[columns[i]].ToString() + "\"";

                if (i < length - 1)
                    res += ",";
            }

            res += "}";
        }

        res += "}";

        return res;
    }