以编程方式在任意位置从头开始创建DB

Question

我正在制作一个使用SQL Server Express/LocalDB的简单桌面应用程序。我在任意非特权位置有一个数据目录，我想在其中创建一个数据库文件。我最初创建了数据库并生成了一个模型供EF使用;现在我想使用该模型在我需要的任何地方重新创建数据库。

我发现了各种帖子做类似的，但他们似乎是删除和重新创建一个现有的数据库通过一个上下文，开始工作，用于测试目的。我想从一个空目录开始。

使用这里代码的摘录，我能够在磁盘上物理地创建数据库文件，使用SQL语句创建新的.mdf和.ldf文件。但他们没有图式;如果我从.mdf文件启动一个上下文实例，然后尝试计数表中的行数，我会得到一个异常，因为表不存在。

如果我尝试调用ctx.Database.Create()，然后我得到数据库无法创建的错误，因为它已经存在。当然有，只是没有表格。

如果我最初不使用原始SQL查询来创建新的空数据库，并且我尝试如下创建上下文，其中filespec指向有效目录中不存在的.mdf文件，.Create()总是抛出异常" database "无法创建，因为它已经存在"

string connectionString
        = "Data Source=(LocalDB)\v11.0;AttachDbFilename="
        + fileSpec;
EventsListDBEntities ctx = new EventsListDBEntities();
ctx.Database.Connection.ConnectionString = connectionString;
ctx.Database.Create();
ctx.Database.Initialize(true);

如何让EF在我的空DB中创建表，或者从头开始创建文件?

Answer 1

试着使用下面的代码:

string connectionString
        = "Data Source=(LocalDB)\v11.0;AttachDbFilename="
        + fileSpec;
EventsListDBEntities ctx = new EventsListDBEntities();
ctx.Database.Connection.ConnectionString = connectionString;
ctx.Database.CreateIfNotExists(); // Change this line.
ctx.Database.Initialize(true);

https://msdn.microsoft.com/en-us/library/system.data.entity.database.createifnotexists%28v=vs.113%29.aspx M: System.Data.Entity.Database.CreateIfNotExists

Answer 2

经过多次试验，我最终得到了这样的代码:

string connectionString
      = "Data Source=(LocalDB)\v11.0;AttachDbFilename="
      + fileSpec + ";database=EventsListDB";
/* We can't go straight into the context and create the DB because 
 * it needs a connection to "master" and can't create it. Although this
 * looks completely unrelated, under the hood it leaves behind something
 * that EF can pick up and use- and it can't hurt to delete any references 
 * to databases of the same name that may be lurking in other previously
 * used directories.
 */
SqlConnectionStringBuilder masterCSB = new SqlConnectionStringBuilder(connectionString);
masterCSB.InitialCatalog = "master";
masterCSB.AttachDBFilename = "";
using (var sqlConn = new SqlConnection(masterCSB.ToString()))
{
    sqlConn.Open();
    using (var cmd = sqlConn.CreateCommand())
    {
        bool done = false;
        int attempt = 0;
        do
        {
            try
            {
                cmd.CommandText =
                    String.Format(
                        "IF EXISTS (Select name from sys.databases " + 
                        "WHERE name = '{0}') " +
                        "DROP DATABASE {0}", "EventsListDB");
                cmd.ExecuteNonQuery();
                done = true;
            }
            catch (System.Exception ex)
            {
                /* We sometimes get odd exceptions that're probably because LocalDB hasn't finished starting. */
                if (attempt++ > 5)
                {
                    throw ex;
                }
                else Thread.Sleep(100);
            }
        } while (!done);
    }
}
/* Now we can create the context and use that to create the DB. Note that
 * a custom constructor's been added to the context exposing the base
 * constructor that can take a connection string- changing the connection
 * string after the default constructor reads it from App.config isn't 
 * sufficient.
 */
EventsListDBEntities ctx = new EventsListDBEntities(connectionString);
ctx.Database.Create();
int numRecords = ctx.EventLists.Count(); //See if it really worked.