实体框架 CTP 4 - Code First 自定义数据库初始值设定项 [英] Entity Framework CTP 4 - Code First Custom Database Initializer
问题描述
我想实现一个自定义数据库初始化策略，以便我可以生成数据库架构并使用提供的用户 ID 和密码将其应用到 EXISTING EMPTY SQL 数据库.
I would like to implement a custom database initialization strategy so that I can generate the database schema and apply it to an EXISTING EMPTY SQL database using a supplied User ID and Password.
遗憾的是，内置策略无法满足我的需求:
Unfortunately the built-in strategies don’t provide what I’m looking for:
// The default strategy creates the DB only if it doesn't exist - but it does
// exist so this does nothing
Database.SetInitializer(new CreateDatabaseOnlyIfNotExists<DataContext>());
// Drops and re-creates the database but then this breaks my security mapping and
// only works if using a "Trusted" connection
Database.SetInitializer(new RecreateDatabaseIfModelChanges<DataContext>());
// Strategy for always recreating the DB every time the app is run. – no good for
// what I want
Database.SetInitializer(new AlwaysRecreateDatabase<DataContext>());
我已计算出以下内容，但这不会创建 ModelHash，因此我无法使用 "context.Database.ModelMatchesDatabase()" 来验证数据库架构是否已创建并防止多次初始化:
I have worked out the following but this does not create the ModelHash so I’m unable to use "context.Database.ModelMatchesDatabase()" to validate that the database schema has been created and prevent multiple initializations:
public class Initializer : IDatabaseInitializer<DataContext>
{
Public void InitializeDatabase(DataContext context)
{
// this generates the SQL script from my POCO Classes
var sql = context.ObjectContext.CreateDatabaseScript();
// As expected - when run the second time it bombs out here with "there is already an
// object named xxxxx in the database"
context.ObjectContext.ExecuteStoreCommand(sql);
this.seed(context)
context.SaveChanges();
}
}
问题:
有谁知道我如何获取/创建模型哈希?(这是一个 EdmMetadata 实体)
Does anyone know how I can get/create the model hash? (which is an EdmMetadata Entity)
-或-
一般来说，使用 Code First CTP 有没有更好的方法来做到这一点?
Is there a better way of doing this in general using the Code First CTP?
推荐答案
我遇到了同样的问题.我并没有真正解决它，但我设法运行了一些令人讨厌的解决方法，因此我可以将我的解决方案部署到 AppHarbor ;)
I ran into the same problem. I didn't really solve it, but I managed to get a little nasty workaround running, so i can deploy my solution to AppHarbor ;)
它是一个 IDatabaseInitializer 实现，它不会删除数据库，而只是对所有约束和表进行核处理，然后使用 ObjectContext.CreateDatabaseScript() 方法生成 sql，然后我将其作为 storecommand 执行.很像问题中的上述实现.
Its a IDatabaseInitializer implementation, that doesn't delete the db, but just nukes all the constraints and tables, and then uses the ObjectContext.CreateDatabaseScript() method to generate the sql, and then I execute it as a storecommand. A lot like the above implementation in the question.
但我还添加了从模型创建哈希并将其保存在 db 中的功能，当它再次运行时，它会检查当前模型哈希是否与 i db 匹配.就像真正的代码优先实现一样.
But i also added functionality to create a hash from the model and save it in db, and when it runs again it checks if the current model-hash matches the one i db. Just like the real code-first implementation.
我无法使其与 context.Database.CompatibleWithModel(true) 中的构建一起使用 - 但这应该也能正常工作，并且将其视为临时解决方法应该没问题.
I couldn't make it work with the build in context.Database.CompatibleWithModel(true) - but this should work just as well, and seeing as its a temporary workaround it should be fine.
using System;
using System.Data.Entity;
using System.Data.Entity.Database;
using System.Data.Entity.Design;
using System.Data.Entity.Infrastructure;
using System.Data.Metadata.Edm;
using System.Data.Objects;
using System.Globalization;
using System.Security.Cryptography;
using System.Text;
using System.Xml;
using System.Linq;
namespace Devtalk
{
public class DontDropDbJustCreateTablesIfModelChanged<T> : IDatabaseInitializer<T> where T : DbContext
{
private EdmMetadata _edmMetaData;
public void InitializeDatabase(T context)
{
ObjectContext objectContext = ((IObjectContextAdapter)context).ObjectContext;
string modelHash = GetModelHash(objectContext);
if (CompatibleWithModel(modelHash, context, objectContext)) return;
DeleteExistingTables(objectContext);
CreateTables(objectContext);
SaveModelHashToDatabase(context, modelHash, objectContext);
}
private void SaveModelHashToDatabase(T context, string modelHash, ObjectContext objectContext)
{
if (_edmMetaData != null) objectContext.Detach(_edmMetaData);
_edmMetaData = new EdmMetadata();
context.Set<EdmMetadata>().Add(_edmMetaData);
_edmMetaData.ModelHash = modelHash;
context.SaveChanges();
}
private void CreateTables(ObjectContext objectContext)
{
string dataBaseCreateScript = objectContext.CreateDatabaseScript();
objectContext.ExecuteStoreCommand(dataBaseCreateScript);
}
private void DeleteExistingTables(ObjectContext objectContext)
{
objectContext.ExecuteStoreCommand(Dropallconstraintsscript);
objectContext.ExecuteStoreCommand(Deletealltablesscript);
}
private string GetModelHash(ObjectContext context)
{
var csdlXmlString = GetCsdlXmlString(context).ToString();
return ComputeSha256Hash(csdlXmlString);
}
private bool CompatibleWithModel(string modelHash, DbContext context, ObjectContext objectContext)
{
var isEdmMetaDataInStore = objectContext.ExecuteStoreQuery<int>(LookupEdmMetaDataTable).FirstOrDefault();
if (isEdmMetaDataInStore == 1)
{
_edmMetaData = context.Set<EdmMetadata>().FirstOrDefault();
if (_edmMetaData != null)
{
return modelHash == _edmMetaData.ModelHash;
}
}
return false;
}
private string GetCsdlXmlString(ObjectContext context)
{
if (context != null)
{
var entityContainerList = context.MetadataWorkspace.GetItems<EntityContainer>(DataSpace.SSpace);
if (entityContainerList != null)
{
EntityContainer entityContainer = entityContainerList.FirstOrDefault();
var generator = new EntityModelSchemaGenerator(entityContainer);
var stringBuilder = new StringBuilder();
var xmlWRiter = XmlWriter.Create(stringBuilder);
generator.GenerateMetadata();
generator.WriteModelSchema(xmlWRiter);
xmlWRiter.Flush();
return stringBuilder.ToString();
}
}
return string.Empty;
}
private static string ComputeSha256Hash(string input)
{
byte[] buffer = new SHA256Managed().ComputeHash(Encoding.ASCII.GetBytes(input));
var builder = new StringBuilder(buffer.Length * 2);
foreach (byte num in buffer)
{
builder.Append(num.ToString("X2", CultureInfo.InvariantCulture));
}
return builder.ToString();
}
private const string Dropallconstraintsscript =
@"select
'ALTER TABLE ' + so.table_name + ' DROP CONSTRAINT ' + so.constraint_name
from INFORMATION_SCHEMA.TABLE_CONSTRAINTS so";
private const string Deletealltablesscript =
@"declare @cmd varchar(4000)
declare cmds cursor for
Select
'drop table [' + Table_Name + ']'
From
INFORMATION_SCHEMA.TABLES
open cmds
while 1=1
begin
fetch cmds into @cmd
if @@fetch_status != 0 break
print @cmd
exec(@cmd)
end
close cmds
deallocate cmds";
private const string LookupEdmMetaDataTable =
@"Select COUNT(*)
FROM INFORMATION_SCHEMA.TABLES T
Where T.TABLE_NAME = 'EdmMetaData'";
}
}
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