Dapper parameters not working

Question

I'm trying to use the Dapper orm with the following simple query:

var sqlString = new StringBuilder();
sqlString.Append("select a.acct AccountNumber,");
sqlString.Append("       b.first_name FirstName,");
sqlString.Append("       b.last_name LastName,");
sqlString.Append("       a.rr RrNumber,");
sqlString.Append("       c.addr1 AddressLine1,");
sqlString.Append("       c.addr2 AddressLine2,");
sqlString.Append("       c.addr3 AddressLine3,");
sqlString.Append("       c.addr4 AddressLine4,");
sqlString.Append("       c.addr5 AddressLine5,");
sqlString.Append("       c.addr6 AddressLine6,");
sqlString.Append("       c.addr7 AddressLine7,");
sqlString.Append("       c.addr8 AddressLine8 ");
sqlString.Append("from (pub.mfclac as a left join pub.mfcl as b on a.client=b.client) ");
sqlString.Append("left join pub.mfclad as c on a.client=c.client ");
sqlString.Append("where a.acct = '@ZYX'");

var connection = new OdbcConnection(_connectionString);

var result = connection.Query(sqlString.ToString(),
    new
    {
        ZYX = accountNumber
    });            

However when I execute this with an accountNumber known to exist, dapper returns nothing. So I tried to remove the quotes to verify that the parameter is in fact being replaced with the account number, however the error being returned from the server indicates a syntax error around "@ZYX". Which means dapper is not replacing the parameter with it's given value. Any ideas why this is happening? From the limited documentation out there, this should 'just work'.

---

Edit1

Couldn't get this to work. Using string.format to insert the parameter as a work around.

Answer 1

There are two issues here; firstly (although you note this in your question) where a.acct = '@ZYX', under SQL rules, does not make use of any parameter - it looks to match the literal string that happens to include an @ sign. For SQL-Server (see note below), the correct usage would be where a.acct = @ZYX.

However! Since you are use OdbcConnection, named parameters do not apply. If you are actually connecting to something like SQL-Server, I would strongly recommend using the pure ADO.NET clients, which have better features and performance than ODBC. However, if ODBC is your only option: it does not use named parameters. Until a few days ago, this would have represented a major problem, but as per Passing query parameters in Dapper using OleDb, the code (but not yet the NuGet package) now supports ODBC. If you build from source (or wait for the next release), you should be able to use:

...
where a.acct = ?

in your command, and:

var result = connection.Query(sqlString.ToString(),
new {
    anythingYouLike = accountNumber
});

Note that the name (anythingYouLike) is not used by ODBC, so can be... anything you like. In a more complex scenario, for example:

.Execute(sql, new { id = 123, name = "abc", when = DateTime.Now });

dapper uses some knowledge of how anonymous types are implemented to understand the original order of the values, so that they are added to the command in the correct sequence (id, name, when).

One final observation:

Which means dapper is not replacing the parameter with it's given value.

Dapper never replaces parameters with their given value. That is simply not the correct way to parameterize sql: the parameters are usually sent separately, ensuring:

• there is no SQL injection risk
• maximum query plan re-use
• no issues of formatting

Note that some ADO.NET / ODBC providers could theoretically choose to implement things internally via replacement - but that is separate to dapper.

Answer 2

I landed here from dublicate question: Dapper must declare the scalar variable

Error: Must declare the scalar variable "@Name".

I created queries dynamically with this piece of code:

public static bool Insert<T>(T entity)
        {
            var tableName = entity.GetType().CustomAttributes.FirstOrDefault(x => x.AttributeType.Name == nameof(TableAttribute))?.ConstructorArguments?.FirstOrDefault().Value as string;
            if (string.IsNullOrEmpty(tableName))
                throw new Exception($"Cannot save {entity.GetType().Name}. Database models should have [Table(\"tablename\")] attribute.");
            DBSchema.TryGetValue(tableName.ToLower(), out var fields);
            using (var con = new SqlConnection(ConnectionString))
            {
                con.Open();

                var sql = $"INSERT INTO [{tableName}] (";
                foreach (var field in fields.Where(x => x != "id")) 
                {
                    sql += $"[{field}]"+",";
                }
                sql = sql.TrimEnd(',');
                sql += ")";
                sql += " VALUES (";
                foreach (var field in fields.Where(x => x != "id"))
                {
                    sql += "@"+field + ",";
                }
                sql = sql.TrimEnd(',');
                sql += ")";

                var affectedRows = con.Execute(sql, entity);
                return affectedRows > 0;
            }
        }

And I got the same error when my models was like this:

[Table("Users")]
public class User
{
   public string Name;
   public string Age;
}

I changed them to this:

[Table("Users")]
public class User
{
    public string Name { get; set; }
    public string Age { get; set; }
}

And it solved the problem for me.