问题描述：
CodeSmith是现在比较实用的代码生成器，但是我们发现一个问题：
使用CodeSmith编写MySQL模板的时候，会发现一个问题：MySQL数据表中的列说明获取不到，也就是column.Description。如图：
我们打开CodeSmith编写一个简单的Model实体类的示例模板如下：
<%--
Name: MySQL Model实体模板
Author: 孤影[QQ:]
Description: CodeSmith连接MySQL生成Model实体模板
--%>
<%@ Template Language="C#" TargetLanguage="C#" ResponseEncoding="UTF-8" %>
<%@ Assembly Name="SchemaExplorer" %>
<%@ Import Namespace="SchemaExplorer" %>
<%@ Property Name="SourceTable" Type="SchemaExplorer.TableSchema" Description="目标数据表" %>
<%@ Property Name="ModelNamespace" Type="System.String" Description="Model实体所在的命名空间" %>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace <%=ModelNamespace %>
{
/// <summary>
/// <%=SourceTable.Description %>
/// </summary>
public class <%=SourceTable.Name %>
{
<%
// 循环遍历 获取当前数据表中的所有列
foreach(ColumnSchema column in SourceTable.Columns){
Response.WriteLine(string.Format("// {0}",column.Description));
Response.WriteLine(string.Format("public {0} {1} ;",GetCSharpVariableType(column),column.Name));
}
%>
}
}
<script runat="template">
// 获取指定列对应的C#数据类型
public string GetCSharpVariableType(ColumnSchema column)
{
if (column.Name.EndsWith("TypeCode")) return column.Name;
switch (column.DataType)
{
case DbType.AnsiString: return "string";
case DbType.AnsiStringFixedLength: return "string";
case DbType.Binary: return "byte[]";
case DbType.Boolean: return "bool";
case DbType.Byte: return "byte";
case DbType.Currency: return "decimal";
case DbType.Date: return "DateTime";
case DbType.DateTime: return "DateTime";
case DbType.Decimal: return "decimal";
case DbType.Double: return "double";
case DbType.Guid: return "Guid";
case DbType.Int16: return "short";
case DbType.Int32: return "int";
case DbType.Int64: return "long";
case DbType.Object: return "object";
case DbType.SByte: return "sbyte";
case DbType.Single: return "float";
case DbType.String: return "string";
case DbType.StringFixedLength: return "string";
case DbType.Time: return "TimeSpan";
case DbType.UInt16: return "ushort";
case DbType.UInt32: return "uint";
case DbType.UInt64: return "ulong";
case DbType.VarNumeric: return "decimal";
default:
{
return "__UNKNOWN__" + column.NativeType;
}
}
}
</script>
一个简单的CodeSmith生成Model实体的模板
然后我们点击生成，生成的代码如下图：
当然，使用SQL Server及其他数据库都是可以获取到的，这是为什么呢？
逼的没招没招了的时候，果断打开.NET Reflector，看看CodeSmith对SQL Server和MySQL二者，数据表生成操作的时候，有什么不同的地方，或者有什么缺少的地方。
CodeSmith中对MySQL操作的DLL组件位置是：“X:\...\CodeSmith\v7.0\SchemaProviders\SchemaExplorer.MySQLSchemaProvider.dll”
展开后，开始一个个找里面的方法，突然发现一个亮点：“GetTableColumns(string connectionString, TableSchema table);”
这个字面的意思不就是获取列数据么？打开看看。。。可惜，里面只是根据表查询所有列，并没有Description相关操作。
继续找，继续对比。。。最终终于找到问题了：
方法“GetExtendedProperties(string connectionString, SchemaObjectBase schemaObject);”里面的查询语句是：
string str = string.Format("SELECT EXTRA, COLUMN_DEFAULT, COLUMN_TYPE FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = '{0}' AND TABLE_NAME = '{1}' AND COLUMN_NAME = '{2}'", schema.Table.Database.Name, schema.Table.Name, schema.Name);
这个不就是获取Column列中的扩展属性的方法么？！
对比发现，SQL Server的dll里这个方法的下面，有返回Description，而MySQL正好没有！
二话不说，找到CodeSmith的源码包解压，翻出MySQL的项目：“X:\...\CodeSmith\v7.0\Samples\Samples\Projects\CSharp\MySQLSchemaProvider”
然后打开Visual Studio载入"MySQLSchemaProvider.csproj"，有很多错误，那是因为缺少了引用，添加CodeSmith\bin里面的相关引用即可。
需要引用的组件你可以在下面两个CodeSmith安装目录中找到：
“X:\...\CodeSmith\v7.0\bin\”、“X:\...\CodeSmith\v7.0\AddIns\”
添加引用之后，错误就全部没了：
然后我们果断开始修改代码、首先找到刚刚那个获取列扩展属性的方法：
“public ExtendedProperty[] GetExtendedProperties(string connectionString, SchemaObjectBase schemaObject)”
然后我们根据观察SQL Server的代码，发现MySQL里面这个方法：
在SQL语句查询的时候少查询了一项数据：“COLUMN_COMMENT”，于是我们首先修改它查询的SQL语句如下：
string commandText = string.Format(@"SELECT EXTRA, COLUMN_DEFAULT, COLUMN_TYPE, COLUMN_COMMENT
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = '{0}' AND TABLE_NAME = '{1}' AND COLUMN_NAME = '{2}'",
columnSchema.Table.Database.Name, columnSchema.Table.Name, columnSchema.Name);
既然上面查询了，按照正常的数据查询流程，下面应该遍历读取，然后返回吧？
于是继续看，下面有一个while，正是将上面查询出来的数据返回的，我们对比SQL Server的代码发现：
上面查询出来的每一项，下面都有获取返回，而我们刚刚添加的那个“COLUMN_COMMENT”则没有进行数据获取、没有怎么办？加呗~
获取每个数据后，最后统一将封装在“extendedProperties”中，于是我们也将获取到的Description添加进去，其与步骤省略。最终修改的代码如下：
public ExtendedProperty[] GetExtendedProperties(string connectionString, SchemaObjectBase schemaObject)
{
List<ExtendedProperty> extendedProperties = new List<ExtendedProperty>();
if (schemaObject is ColumnSchema)
{
ColumnSchema columnSchema = schemaObject as ColumnSchema;
string commandText = string.Format(@"SELECT EXTRA, COLUMN_DEFAULT, COLUMN_TYPE, COLUMN_COMMENT
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = '{0}' AND TABLE_NAME = '{1}' AND COLUMN_NAME = '{2}'",
columnSchema.Table.Database.Name, columnSchema.Table.Name, columnSchema.Name);
using (DbConnection connection = CreateConnection(connectionString))
{
connection.Open();
DbCommand command = connection.CreateCommand();
command.CommandText = commandText;
command.Connection = connection;
using (IDataReader reader = command.ExecuteReader(CommandBehavior.CloseConnection))
{
while (reader.Read())
{
).ToLower();
);
string columndefault = "";
if (!columndefaultisnull)
{
columndefault = reader.GetString().ToUpper();
}
).ToUpper();
);
);
extendedProperties.Add(new ExtendedProperty(ExtendedPropertyNames.IsIdentity, isIdentity, columnSchema.DataType));
if (isIdentity)
{
/*
MySQL auto_increment doesn't work exactly like SQL Server's IDENTITY
I believe that auto_increment is equivalent to IDENTITY(1, 1)
However, auto_increment behaves differently from IDENTITY when used
with multi-column primary keys. See the MySQL Reference Manual for details.
*/
extendedProperties.Add(, columnSchema.DataType));
extendedProperties.Add(, columnSchema.DataType));
}
extendedProperties.Add(new ExtendedProperty("CS_ColumnDefaultIsNull", columndefaultisnull, DbType.Boolean)); // Added for Backwards Compatibility.
extendedProperties.Add(new ExtendedProperty(ExtendedPropertyNames.DefaultValue, columndefault, DbType.String));
extendedProperties.Add(new ExtendedProperty("CS_ColumnDefault", columndefault, DbType.String)); // Added for Backwards Compatibility.
extendedProperties.Add(new ExtendedProperty(ExtendedPropertyNames.SystemType, columntype, DbType.String));
extendedProperties.Add(new ExtendedProperty("CS_ColumnType", columntype, DbType.String)); // Added for Backwards Compatibility.
extendedProperties.Add(new ExtendedProperty("CS_ColumnExtra", extra.ToUpper(), DbType.String));
extendedProperties.Add(new ExtendedProperty("CS_Description", columncomment, DbType.String));
}
if (!reader.IsClosed)
reader.Close();
}
if (connection.State != ConnectionState.Closed)
connection.Close();
}
}
if (schemaObject is TableSchema)
{
TableSchema tableSchema = schemaObject as TableSchema;
string commandText = string.Format(@"SHOW CREATE TABLE `{0}`.`{1}`", tableSchema.Database.Name, tableSchema.Name);
using (DbConnection connection = CreateConnection(connectionString))
{
connection.Open();
DbCommand command = connection.CreateCommand();
command.CommandText = commandText;
command.Connection = connection;
using (IDataReader reader = command.ExecuteReader(CommandBehavior.CloseConnection))
{
while (reader.Read())
{
);
extendedProperties.Add(new ExtendedProperty("CS_CreateTableScript", createtable, DbType.String));
}
if (!reader.IsClosed)
reader.Close();
}
if (connection.State != ConnectionState.Closed)
connection.Close();
}
}
return extendedProperties.ToArray();
}
最终修改完成的“GetExtendedProperties”方法
然后我们F6生成一个修改后的dll组件"SchemaExplorer.MySQLSchemaProvider.dll"。
找到默认的dll：“X:\...\CodeSmith\v7.0\SchemaProviders\SchemaExplorer.MySQLSchemaProvider.dll”，替.....不行，还是先备份一下。。。哈哈
然后替换。打开重启CodeSmith，再次生成。。。-_-# 我去！这是在逗我么。
再次回到Visual Studio中仔细看看整个方法，最后发现。。服了。它的这个方法的判断逻辑是：
public ExtendedProperty[] GetExtendedProperties(string connectionString, SchemaObjectBase schemaObject)
{
List<要返回的东西>......
if(schemaObject 是一个 ColumnSchema)// 如果是一个列对象
{
// 这里面也就是我们刚刚改的，获取列说明部分的代码
}
if(schemaObject 是一个 TableSchema)// 完全没有注意下面的这个判断，如果是一个表对象！！！
{
// 这里也就是我们下面要动手脚的地方了。
}
}
废话不多说。直接上这个方法最终的代码：
public ExtendedProperty[] GetExtendedProperties(string connectionString, SchemaObjectBase schemaObject)
{
List<ExtendedProperty> extendedProperties = new List<ExtendedProperty>();
if (schemaObject is ColumnSchema)
{
ColumnSchema columnSchema = schemaObject as ColumnSchema;
string commandText = string.Format(@"SELECT EXTRA, COLUMN_DEFAULT, COLUMN_TYPE, COLUMN_COMMENT
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = '{0}' AND TABLE_NAME = '{1}' AND COLUMN_NAME = '{2}'",
columnSchema.Table.Database.Name, columnSchema.Table.Name, columnSchema.Name);
using (DbConnection connection = CreateConnection(connectionString))
{
connection.Open();
DbCommand command = connection.CreateCommand();
command.CommandText = commandText;
command.Connection = connection;
using (IDataReader reader = command.ExecuteReader(CommandBehavior.CloseConnection))
{
while (reader.Read())
{
).ToLower();
);
string columndefault = "";
if (!columndefaultisnull)
{
columndefault = reader.GetString().ToUpper();
}
).ToUpper();
);
);
extendedProperties.Add(new ExtendedProperty(ExtendedPropertyNames.IsIdentity, isIdentity, columnSchema.DataType));
if (isIdentity)
{
/*
MySQL auto_increment doesn't work exactly like SQL Server's IDENTITY
I believe that auto_increment is equivalent to IDENTITY(1, 1)
However, auto_increment behaves differently from IDENTITY when used
with multi-column primary keys. See the MySQL Reference Manual for details.
*/
extendedProperties.Add(, columnSchema.DataType));
extendedProperties.Add(, columnSchema.DataType));
}
extendedProperties.Add(new ExtendedProperty("CS_ColumnDefaultIsNull", columndefaultisnull, DbType.Boolean)); // Added for Backwards Compatibility.
extendedProperties.Add(new ExtendedProperty(ExtendedPropertyNames.DefaultValue, columndefault, DbType.String));
extendedProperties.Add(new ExtendedProperty("CS_ColumnDefault", columndefault, DbType.String)); // Added for Backwards Compatibility.
extendedProperties.Add(new ExtendedProperty(ExtendedPropertyNames.SystemType, columntype, DbType.String));
extendedProperties.Add(new ExtendedProperty("CS_ColumnType", columntype, DbType.String)); // Added for Backwards Compatibility.
extendedProperties.Add(new ExtendedProperty("CS_ColumnExtra", extra.ToUpper(), DbType.String));
extendedProperties.Add(new ExtendedProperty("CS_Description", columncomment, DbType.String));
}
if (!reader.IsClosed)
reader.Close();
}
if (connection.State != ConnectionState.Closed)
connection.Close();
}
}
if (schemaObject is TableSchema)
{
TableSchema tableSchema = schemaObject as TableSchema;
string commandText = string.Format(@"SHOW CREATE TABLE `{0}`.`{1}`", tableSchema.Database.Name, tableSchema.Name);
using (DbConnection connection = CreateConnection(connectionString))
{
connection.Open();
DbCommand command = connection.CreateCommand();
command.CommandText = commandText;
command.Connection = connection;
using (IDataReader reader = command.ExecuteReader(CommandBehavior.CloseConnection))
{
while (reader.Read())
{
);
extendedProperties.Add(new ExtendedProperty("TS_Description", createtable, DbType.String));
int engineIndex = createtable.LastIndexOf("ENGINE");
int commentIndex = createtable.LastIndexOf("COMMENT=");
);
if (commentIndex > engineIndex)
{
tableDescription = createtable.Substring(commentIndex + ).Replace("'", "");
}
extendedProperties.Add(new ExtendedProperty("CS_Description", tableDescription, DbType.String));
}
if (!reader.IsClosed)
reader.Close();
}
if (connection.State != ConnectionState.Closed)
connection.Close();
}
}
return extendedProperties.ToArray();
}
最终的“GetExtendedProperties”方法
重新生成，替换。。。重启CodeSmith，链接MySQL生成。。。。必然果断Ok：
网上当然也有很多例子，不过都是只处理了列的说明，没有处理表的说明。
我这个处理表说明是通过截取已获得的CreateTableScript里面的数据，获取的表说明。
码字不容易，感觉不错的话，请不要忘了点赞哦~(*^_^ *)
【本章来自 孤影'Blog：http://www.cnblogs.com/LonelyShadow，码字不容易，转载请注明出处。】