将复杂类型的 C# 转换为 YAML

Question

我是 YAML 的初学者，正在研究如何将 YAML 解析为 C#。在这里，我试图解析 C# 对象模块，其中我有复杂对象类型的数据，例如 C# 中的 DataTable 类或 Type 类。 我知道如何使用 YAMLDotNet 库转换基本类型，但真的不知道如何对这些类型做同样的事情。 请帮忙。

Answer 1

DataTable 是一个失去属性的复杂对象。最简单的方法是将与您相关的数据提取到更简单的数据结构中，然后将其序列化。但是，如果您真的愿意，您可以创建自定义 IYamlTypeConverter。下面是一个示例，它将序列化表的列名和类型，以及行的值：

public class DataTableTypeConverter : IYamlTypeConverter
{
    public bool Accepts(Type type)
    {
        return typeof(DataTable).IsAssignableFrom(type);
    }

    public object ReadYaml(IParser parser, Type type)
    {
        var table = new DataTable();

        parser.Expect<MappingStart>();

        ReadColumns(parser, table);
        ReadRows(parser, table);

        parser.Expect<MappingEnd>();

        return table;
    }

    private static void ReadColumns(IParser parser, DataTable table)
    {
        var columns = parser.Expect<Scalar>();
        if (columns.Value != "columns")
        {
            throw new YamlException(columns.Start, columns.End,
                                    "Expected a scalar named 'columns'");
        }

        parser.Expect<MappingStart>();
        while (parser.Allow<MappingEnd>() == null)
        {
            var columnName = parser.Expect<Scalar>();
            var typeName = parser.Expect<Scalar>();

            table.Columns.Add(columnName.Value, Type.GetType(typeName.Value));
        }
    }

    private static void ReadRows(IParser parser, DataTable table)
    {
        var columns = parser.Expect<Scalar>();
        if (columns.Value != "rows")
        {
            throw new YamlException(columns.Start, columns.End,
                                    "Expected a scalar named 'rows'");
        }

        parser.Expect<SequenceStart>();
        while (parser.Allow<SequenceEnd>() == null)
        {
            var row = table.NewRow();

            var columnIndex = 0;
            parser.Expect<SequenceStart>();
            while (parser.Allow<SequenceEnd>() == null)
            {
                var value = parser.Expect<Scalar>();
                var columnType = table.Columns[columnIndex].DataType;
                row[columnIndex] = TypeConverter.ChangeType(value.Value, columnType);
                ++columnIndex;
            }

            table.Rows.Add(row);
        }
    }

    public void WriteYaml(IEmitter emitter, object value, Type type)
    {
        var table = (DataTable)value;
        emitter.Emit(new MappingStart());

        EmitColumns(emitter, table);
        EmitRows(emitter, table);

        emitter.Emit(new MappingEnd());
    }

    private static void EmitColumns(IEmitter emitter, DataTable table)
    {
        emitter.Emit(new Scalar("columns"));
        emitter.Emit(new MappingStart(null, null, true, MappingStyle.Block));
        foreach (DataColumn column in table.Columns)
        {
            emitter.Emit(new Scalar(column.ColumnName));
            emitter.Emit(new Scalar(column.DataType.AssemblyQualifiedName));
        }
        emitter.Emit(new MappingEnd());
    }

    private static void EmitRows(IEmitter emitter, DataTable table)
    {
        emitter.Emit(new Scalar("rows"));
        emitter.Emit(new SequenceStart(null, null, true, SequenceStyle.Block));

        foreach (DataRow row in table.Rows)
        {
            emitter.Emit(new SequenceStart(null, null, true, SequenceStyle.Flow));
            foreach (var item in row.ItemArray)
            {
                var value = TypeConverter.ChangeType<string>(item);
                emitter.Emit(new Scalar(value));
            }
            emitter.Emit(new SequenceEnd());
        }

        emitter.Emit(new SequenceEnd());
    }
}

用法如下：

var table = new DataTable();
table.Columns.Add("id", typeof(int));
table.Columns.Add("name", typeof(string));
table.Columns.Add("description", typeof(string));

table.Rows.Add(1, "first", "The first row");
table.Rows.Add(2, "second", "The second row");

// Serialize
var serializer = new SerializerBuilder()
    .WithTypeConverter(new DataTableTypeConverter())
    .Build();

var yaml = serializer.Serialize(table);

// Deserialize
var deserializer = new DeserializerBuilder()
    .WithTypeConverter(new DataTableTypeConverter())
    .Build();

var parsedTable = deserializer.Deserialize<DataTable>(yaml);

本例中的序列化 YAML 为：

columns:
  id: System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
  name: System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
  description: System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
rows:
- [1, first, The first row]
- [2, second, The second row]