如何使用C＃确定SQL Server CE表中是否存在列？

Question

遗留代码以这种方式执行：

public bool isValidField(string tableName, string fieldName)
{
    bool retVal;
    string tblQuery = string.Format("SELECT {0} FROM {1}", fieldName, tableName);
    checkConnection();
    try
    {
        SqlCeCommand cmd = objCon.CreateCommand();
        cmd.CommandText = tblQuery;
        object objvalid = cmd.ExecuteScalar();
        retVal = (null != objvalid);
    }
    catch
    {
        retVal = false; 
    }
    return retVal;
}

...但我发现它并不总是有效。 在调用该方法并获得false ，一些代码会在表中添加一些列，但是我得到了：

列ID在规范中出现多次。

我在StackOverflow上找到了几个有前途的SQL语句：

if exists(select * from sys.columns 
        where Name = N'columnName' and Object_ID = Object_ID(N'tableName'))  

和

IF COL_LENGTH('table_name','column_name') IS NULL

...但我不确定如何在C＃/ .NET 1.1中实现它

我是否需要使用ExecuteScalar并将返回的值转换为bool？ 或者是其他东西？

UPDATE

改变它并没有纠正问题：

public bool isValidField(string tableName, string columnName)
{
    bool retVal;
    string tblQuery = string.Format(
        "COL_LENGTH({0},{1}) IS NULL",
        tableName,
        columnName);

    checkConnection();
    try
    {
        SqlCeCommand cmd = objCon.CreateCommand();
        cmd.CommandText = tblQuery;
        object objvalid = cmd.ExecuteScalar();
        retVal = Convert.ToBoolean(objvalid);
    }
    catch
    {
        retVal = false; 
    }
    return retVal;
}

更新2

奇怪的是，我用新代码看到了更多这些错误消息。

更新3

当我以这种方式更改代码时没有任何区别：

string tblQuery = "SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS"
                  + " WHERE TABLE_NAME = @tableName AND COLUMN_NAME"
                  + " = @columnName";

checkConnection();
try
{
    SqlCeCommand cmd = objCon.CreateCommand();
    cmd.CommandText = tblQuery;
    SqlCeParameter tblNameParam = new SqlCeParameter(
        "@tableName",
        SqlDbType.NVarChar,
        128);

    tblNameParam.Value = tableName;
    cmd.Parameters.Add(tblNameParam);
    SqlCeParameter colNameParam = new SqlCeParameter(
        "@columnName",
        SqlDbType.NVarChar,
        128);

    colNameParam.Value = tableName;
    cmd.Parameters.Add(colNameParam);
    int i = (int)cmd.ExecuteScalar();
    retVal = i > 0;
}

......所以我不知道哪种方式更可取; 这对我来说似乎更直接......任何想法，任何人？

Answer 1

您只需查询信息架构表即可获得所需信息：

public bool isValidField(string tableName, string columnName)
{
    var tblQuery = "SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS"
                   + " WHERE TABLE_NAME = @tableName AND"
                   + " COLUMN_NAME = @columnName";

    SqlCeCommand cmd = objCon.CreateCommand();
    cmd.CommandText = tblQuery;
    var tblNameParam = new SqlCeParameter(
        "@tableName",
        SqlDbType.NVarChar,
        128);

    tblNameParam.Value = tableName
    cmd.Parameters.Add(tblNameParam);
    var colNameParam = new SqlCeParameter(
        "@columnName",
        SqlDbType.NVarChar,
        128);

    colNameParam.Value = columnName
    cmd.Parameters.Add(colNameParam);
    object objvalid = cmd.ExecuteScalar(); // will return 1 or null
    return objvalid != null;
}

Answer 2

    public bool IsValidField(SqlCeConnection objCon, string tableName, string columnName)
    {
        const string query = "SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS"
                                + " WHERE TABLE_NAME = @TABLENAME AND"
                                + " COLUMN_NAME = @COLUMNNAME";

        using (var cmd = new SqlCeCommand(query, objCon))
        {
            cmd.Parameters.Add("@TABLENAME", SqlDbType.NVarChar, 128).Value = tableName;
            cmd.Parameters.Add("@COLUMNNAME", SqlDbType.NVarChar, 128).Value = columnName;
            var objvalid = cmd.ExecuteScalar(); // will return 1 or null
            return objvalid != null;
        }
    }