Linq To SQL 下实现动态表名的映射

这段时间代码写累了，写几篇文章舒缓一下，也算是劳逸结合吧。如果觉得我的文章对你有用，请给点掌声，谢谢。

提出问题

前段时间，在博客园里看到有位朋友，问如何实现在动态表名。我们都知道，把一个实体类映谢到表里，应该这样写：

using System;
using System.Collections.Generic;
using System.Data.Linq;
using System.Data.Linq.Mapping;
using System.Diagnostics;
using System.Globalization;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Xml.Schema;

namespace ALinq.Mapping
{
class DynamicMappingSource : MappingSource
{
class DynamicAttributedMetaModel : MetaModel
{
private MetaModel source;
private const string TypeName = "System.Data.Linq.Mapping.AttributedMetaModel";

private DynamicMappingSource mappingSource;

internal DynamicAttributedMetaModel(MappingSource mappingSource, Type contextType)
{
this.mappingSource = (DynamicMappingSource)mappingSource;

var bf = BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.CreateInstance;
var args = new object[] { mappingSource, contextType };
source = typeof(DataContext).Assembly.CreateInstance(TypeName, false, bf, null,
args, CultureInfo.CurrentCulture, null) as MetaModel;
Debug.Assert(source != null);
}

public override MetaTable GetTable(Type rowType)
{
if (mappingSource.GetMetaTableName != null)
{
var typeName = "System.Data.Linq.Mapping.AttributedMetaTable";
var bf = BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.CreateInstance;
var attribute = new TableAttribute { Name = mappingSource.GetMetaTableName(rowType) };
var args = new object[] { source, attribute, rowType };
var metaTable = typeof(DataContext).Assembly.CreateInstance(typeName, false, bf, null,
args, CultureInfo.CurrentCulture, null) as MetaTable;
return metaTable;
}
return source.GetTable(rowType);
}

public override MetaFunction GetFunction(MethodInfo method)
{
return source.GetFunction(method);
}

public override IEnumerable<MetaTable> GetTables()
{
return source.GetTables();
}

public override IEnumerable<MetaFunction> GetFunctions()
{
return source.GetFunctions();
}

public override MetaType GetMetaType(Type type)
{
return source.GetMetaType(type);
}

public override MappingSource MappingSource
{
get { return source.MappingSource; }
}

public override Type ContextType
{
get { return source.ContextType; }
}

public override string DatabaseName
{
get { return source.DatabaseName; }
}

public override Type ProviderType
{
get { return source.ProviderType; }
}
}

public Func<Type, string> GetMetaTableName;

protected override MetaModel CreateModel(Type dataContextType)
{
if (dataContextType == null)
{
throw new ArgumentNullException("dataContextType");
}
return new DynamicAttributedMetaModel(this, dataContextType);
}
}

[Table(Name = "User")]
class User
{
[Column]
public int ID;

[Column]
public string Name;

}

class Program
{
static void Main(string[] args)
{
var mappingSource = new DynamicMappingSource();
int i = 0;
mappingSource.GetMetaTableName = delegate(Type type)
{
var att = type.GetCustomAttributes(typeof(TableAttribute), true).Single()
as TableAttribute;
Debug.Assert(att != null);

return att.Name + i;
};
var constr = @"Data Source=NOTEBOOK\SQLEXPRESS;Initial Catalog=DemoDataContext;Integrated Security=True";
var context = new DataContext(constr, mappingSource) { Log = Console.Out };

i = 1;
context.GetTable<User>().Select(o => o).ToList();
i = 2;
context.GetTable<User>().Select(o => o).ToList();
}
}
}

把运行后的结果给大家看一下：



从上图可以看到，表名已经由原来的User分别变为了User1和User2。