C# 以编程方式在任意位置从头开始创建DB

我正在开发一个使用SQLServerExpress/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供EF使用的模型；现在，我想使用该模型在任何需要的地方重新创建数据库

我发现很多帖子都做了类似的工作，但它们似乎是通过一个上下文删除和重新创建一个现有的数据库，这个上下文从一开始就在工作，用于测试目的。我想从一个空目录开始

使用中代码的摘录，我能够在磁盘上物理地创建一个数据库文件，使用SQL语句创建新的.mdf和.ldf文件。但是他们没有模式；如果我从.mdf文件启动一个上下文实例，然后尝试计算表中的行数，就会抛出一个异常，因为表不存在

如果我尝试调用

ctx.Database.Create（）

，则会得到一个错误，即无法创建数据库，因为它已经存在。当然有，只是没有桌子

如果我最初不使用原始SQL查询来创建新的空数据库，并且我尝试按如下方式创建上下文，并且filespec指向有效目录中不存在的.mdf文件，.create（）始终引发异常“无法创建数据库“”，因为它已存在”

---

如何让EF在空数据库中创建表，或从头开始创建文件？

尝试使用以下方法：

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);

---

经过大量的实验，下面是我最终使用的代码

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.

---

Ta，但之前尝试过，因为在这两种情况下它都认为DB存在，

CreateIfNotExists（）

什么也不做，返回false，尽管没有抛出异常，但只要我尝试计算行数，就会在第二种情况下得到“底层提供程序打开失败”，因为没有文件，并且第一种情况下为“对象不存在”或类似，因为数据库已打开，但没有表。

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.