Metah.XXML 元编程语言
Metah.X（简称MX）用自创的语法实现了XML Schema 1.0的语义，并且用C#实现了一个Schema-lized Document Object Model (SDOM)，编译器编译MX代码后将生成使用SDOM的C#代码，这将XML Schema的语义映射到C#上，从而完全释放出XML Schema的力量。尽管现在只有C#版，实现Java版或其它语言版本是完全可能的。
MX是个开源项目，欢迎参与，比如实现Java版或其它语言版本；MX没有定型，欢迎提出修改意见。
XML Schema定义了XML数据（或叫XML实例）的形状及需要遵守的规则，比如下面的XSD代码：
<E1 xmlns="http://ns1"> <E2 A1="123">abc</E2> <E3 xmlns=""> <p:E4 xmlns:p="http://ns2" p:A1="true" A1="123" /> def </E3> </E1>
下面是合法的XML数据：
12345678-33487654321
因为XSD相当繁琐不便于书写，MX自创了用户友好的语法来表达XML Schema的语义，下面的MX代码和上面的XSD代码表达了相同的语义：
//HelloWorld.mxcs
xnamespace {"http://schemas.example.com/projecta"} [namespace: Example.ProjectA] {
type String20 restrict String
facets {
lengthrange: 1..20;
};
;
type PhoneCategory restrict String
facets{
enums: Unknown = "Unknown", Work = "Work", Home = "Home"
};
;
type Phone extend String20
attributes {
attribute Category[?] as PhoneCategory;
};
;
type Customer
attributes {
attribute Name as String20;
attribute Email as
type restrict String20
facets {
patterns: @"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}";
};
;
;
attribute RegistrationDate[?] as DateTime;
};
children {
element Phone[+; membername: Phones] as Phone;
};
;
element Customer as Customer;
}
MX编译器编译HelloWorld.mxcs后，将生成如下的C#代码：
//HelloWorld.mxcs.cs
//Generated by MX compiler
namespace Example.ProjectA
{
public partial class PhoneCategory : ...
{
public static readonly string @Unknown = "Unknown";
public static readonly string @Work = "Work";
public static readonly string @Home = "Home";
...
}
public partial class Phone : ...
{
public partial class AttributeSetClass : ...
{
public string Category_Value { get; set; }
...
}
public AttributeSetClass AttributeSet { get; set; }
public AttributeSetClass EnsureAttributeSet();
public string Value { get; set; }
...
}
public partial class Customer : ...
{
public partial class AttributeSetClass : ...
{
public string Name_Value { get; set; }
public string Email_Value { get; set; }
public DateTime? RegistrationDate_Value { get; set; }
...
}
public AttributeSetClass AttributeSet { get; set; }
public AttributeSetClass EnsureAttributeSet();
public partial class ComplexChildClass : ...
{
public partial class Phones_Class : ...
{
public partial class ItemClass : ...
{
public Phone Type { get; set; }
...
}
public ItemClass CreateAndAddItem();
...
}
public Phones_Class Phones { get; set; }
public Phones_Class Ensure_Phones();
...
}
public ComplexChildClass ComplexChild { get; set; }
public ComplexChildClass EnsureComplexChild();
...
}
public partial class Customer_ElementClass : ...
{
public Customer Type { get; set; }
public static bool TryLoadAndValidate(XmlReader reader, Metah.X.Context context, out Customer_ElementClass result);
...
}
}
使用编译器生成的代码，就可以创建、查询、修改、保存、装载及验证XML数据，下面的手写代码演示了如何使用编译器生成的代码：
//Program.cs
using System;
using System.Xml;//for XmlReader & XmlWriter
using X = Metah.X;
namespace Example.ProjectA {
class Program {
static void Main(string[] args) {
var customer = new Customer();
var cattset = customer.EnsureAttributeSet();
cattset.Name_Value = "Tank";
cattset.Email_Value = "tank@example.com";
cattset.RegistrationDate_Value = DateTime.Now;
var phones = customer.EnsureComplexChild().Ensure_Phones();
var phone = phones.CreateAndAddItem();
phone.EnsureAttributeSet().Category_Value = PhoneCategory.Work;
phone.Value = "12345678-334";
phones.CreateAndAddItem().Value = "87654321";
var customerElement = new Customer_ElementClass { Type = customer };
using (var writer = XmlWriter.Create(@"d:\customer.xml", new XmlWriterSettings { Indent = true }))
customerElement.Save(writer);
//
var ctx = new X.Context();
using (var reader = XmlReader.Create(@"d:\customer.xml")) {
Customer_ElementClass customerElement2;
if (Customer_ElementClass.TryLoadAndValidate(reader, ctx, out customerElement2)) {
var customer2 = customerElement2.Type;
Console.WriteLine("Name={0}, Email={1}, RegistrationDate={2}",
customer2.AttributeSet.Name_Value, customer2.AttributeSet.Email_Value, customer2.AttributeSet.RegistrationDate_Value);
foreach (var phone2 in customer2.ComplexChild.Phones) {
Console.WriteLine("\tCategory={0}, Value={1}", phone2.Type.AttributeSet.Category_Value, phone2.Type.Value);
}
customer2.AttributeSet.Name_Value += "-Knat";
customer2.AttributeSet.RegistrationDate = null;
var phone3 = customer2.ComplexChild.Phones.CreateAndAddItem();
phone3.EnsureAttributeSet().Category_Value = PhoneCategory.Home;
phone3.Value = "11223344";
using (var writer = XmlWriter.Create(@"d:\customer2.xml", new XmlWriterSettings { Indent = true }))
customerElement2.Save(writer);
}
else {
foreach (var diag in ctx.Diagnostics)
Console.WriteLine(diag);
}
}
}
}
}
下面是d:\customer.xml的内容：
12345678-33487654321
下面是d:\customer2.xml的内容：
12345678-3348765432111223344
也就是说，MX的用处 = XML Schema的用处 + Document Object Model的用处。
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