Is it wrong to use braces for variable scope purposes?

Question

I sometimes use braces to isolate a block of code to avoid using by mistake a variable later. For example, when I put several SqlCommands in the same method, I frequently copy-paste blocks of code, ending by mixing the names and executing twice some commands. Adding braces helps to avoid this situation, because using a wrong SqlCommand in a wrong place will result in an error. Here's an illustration:

Collection<string> existingCategories = new Collection<string>();

// Here a beginning of a block
{
    SqlCommand getCategories = new SqlCommand("select Title from Movie.Category where SourceId = @sourceId", sqlConnection, sqlTransaction);
    getCategories.Parameters.AddWithValue("@sourceId", sourceId);
    using (SqlDataReader categoriesReader = getCategories.ExecuteReader(System.Data.CommandBehavior.SingleResult))
    {
        while (categoriesReader.Read())
        {
            existingCategories.Add(categoriesReader["Title"].ToString());
        }
    }
}

if (!existingCategories.Contains(newCategory))
{
    SqlCommand addCategory = new SqlCommand("insert into Movie.Category (SourceId, Title) values (@sourceId, @title)", sqlConnection, sqlTransaction);

    // Now try to make a mistake and write/copy-paste getCategories instead of addCategory. It will not compile.
    addCategory.Parameters.AddWithValue("@sourceId", sourceId);
    addCategory.Parameters.AddWithValue("@title", newCategory);
    addCategory.ExecuteNonQuery();
}

Now, StyleCop displays a warning every time a block follows an empty line. On the other hand, not putting an empty line would make the code much harder to understand.

// Something like:
Collection<string> existingCategories = new Collection<string>();
{
    // Code here
}

// can be understood as (is it easy to notice that semicolon is missing?):
Collection<string> existingCategories = new Collection<string>()
{
    // Code here
}

So,

1. Is there something wrong in using braces to create blocks of code just for variable scope purposes?

2. If it's all right, how to make it more readable without violating StyleCop rules?

Answer 1

There's nothing wrong per se with blocking off code, but you need to consider why you're doing it.

If you're copying and pasting code, you're likely in a situation where you should be refactoring the code and producing functions that you call repeatedly rather than executing similar but different blocks of code repeatedly.

Answer 2

Use the using statement instead of bare brace blocks.

This will avoid the warnings, and also make your code more efficient in terms of resources.

From a larger perspective, you should consider splitting up this method into smaller methods. Using one SqlCommand followed by another is usually better done by calling one method followed by another. Each method would then use their own local SqlCommand.