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是否有方法使用ADO.NET来确定数据库中是否存在与任何数据提供程序一起使用的表?

ado.net sql c#

Ergwun · 技术社区 · 15 年前

我目前正在做这样的事情:

bool DoesTableExist(string tableName)
{
    DbCommand command = this.dbConnection.CreateCommand();
    command.CommandText = "SELECT 1 FROM " + tableName;
    try
    {
        using (DbDataReader reader = command.ExecuteReader())
        {
            return true;
        }
    }
    catch (DbException)
    {
        return false;
    }
}

我希望有一种方法不涉及捕获异常。

2 回复 | 直到 9 年前

Glenn Slayden 9 年前

好吧,你可以用 Connection.GetSchema("TABLES") 方法。

返回一个 DataTable 它将包含数据库中所有表的行。从这里,您可以对照这个检查并查看表是否存在。

然后可以进一步:

    private static bool DoesTableExist(string TableName)
    {
        using (SqlConnection conn = 
                     new SqlConnection("Data Source=DBServer;Initial Catalog=InitialDB;User Id=uname;Password=pword;"))
        {
            conn.Open();

            DataTable dTable = conn.GetSchema("TABLES", 
                           new string[] { null, null, "MyTableName" });

            return dTable.Rows.Count > 0;
        }
    }

如果您使用的是.NET 3.5,那么您也可以将其作为扩展方法。

XDS 9 年前

对Kyle的答案进行了细微改进,因为不同的数据库(例如Oracle和MS SQL Server)将表名列放在“表”表的不同索引中:

    public static bool CheckIfTableExists(this DbConnection connection, string tableName) //connection = ((DbContext) _context).Database.Connection;
    {
        if (connection == null)
            throw new ArgumentException(nameof(connection));

        if (connection.State == ConnectionState.Closed)
            connection.Open();

        var tableInfoOnTables = connection //0
            .GetSchema("Tables")
            .Columns
            .Cast<DataColumn>()
            .Select(x => x.ColumnName?.ToLowerInvariant() ?? "")
            .ToList();

        var tableNameColumnIndex = tableInfoOnTables.FindIndex(x => x.Contains("table".ToLowerInvariant()) && x.Contains("name".ToLowerInvariant())); //order
        tableNameColumnIndex = tableNameColumnIndex == -1 ? tableInfoOnTables.FindIndex(x => x.Contains("table".ToLowerInvariant())) : tableNameColumnIndex; //order
        tableNameColumnIndex = tableNameColumnIndex == -1 ? tableInfoOnTables.FindIndex(x => x.Contains("name".ToLowerInvariant())) : tableNameColumnIndex; //order

        if (tableNameColumnIndex == -1)
            throw new ApplicationException("Failed to spot which column holds the names of the tables in the dictionary-table of the DB");

        var constraints = new string[tableNameColumnIndex + 1];
        constraints[tableNameColumnIndex] = tableName;

        return connection.GetSchema("Tables", constraints)?.Rows.Count > 0;
    }
    //0 different databases have different number of columns and different names assigned to them
    //
    //     SCHEMA,TABLENAME,TYPE -> oracle
    //     table_catalog,table_schema,table_name,table_type -> mssqlserver
    //
    //  we thus need to figure out which column represents the tablename and target that one