How to Correctly Invoke SQL User-Defined Functions (UDFs) from C#?

Incorporating SQL Defined Functions into C# Code: Troubleshooting UDF Invocation

When implementing user-defined SQL functions (UDFs) in C#, developers may encounter issues integrating these functions into their code. One common challenge is correctly calling UDFs from within C# applications.

Consider the following scenario: a developer has defined a TSQL scalar function named Tcupom that calculates the total value of a specific order. To call this function from C#, the developer has written the following code:

public void TotalCupom(int cupom)
{ 
    float SAIDA;           
    SqlDataAdapter da2 = new SqlDataAdapter();
    if (conex1.State == ConnectionState.Closed)
    { 
        conex1.Open();
    }
    SqlCommand Totalf = new SqlCommand("Tcupom", conex1);
    SqlParameter code1 = new SqlParameter("@code", SqlDbType.Int);
    code1.Value = cupom ;
    Totalf.CommandType = CommandType.StoredProcedure ;
    SAIDA = Totalf.ExecuteScalar();

    return SAIDA;
}

However, upon execution, this code fails to retrieve the expected result. To resolve this issue, the developer must address several key concerns within their code:

1. Direct Invocation of UDF:

Directly invoking the UDF name, such as "Tcupom" in the SqlCommand object, is incorrect. To call a UDF from C#, it must be enclosed within an inline SQL statement.

2. CommandType Misconfiguration:

The code incorrectly specifies CommandType.StoredProcedure, implying that the function is a stored procedure. However, UDFs are distinct entities from stored procedures.

3. Missing Database Scope:

In the inline SQL statement, the function name must be fully qualified with the database schema. For example, "SELECT dbo.Tcupom(@code)".

4. Synchronous Invocation:

While the code appears to perform the function invocation asynchronously by assigning the result to SAIDA, the ExecuteScalar() method is inherently synchronous. To perform an asynchronous invocation, use BeginExecuteReader or another asynchronous method.

Corrected Code:

The following corrected code incorporates the necessary changes:

public void TotalCupom(int cupom)
{ 
    float SAIDA;           
    SqlDataAdapter da2 = new SqlDataAdapter();
    if (conex1.State == ConnectionState.Closed)
    {
        conex1.Open();
    }
    SqlCommand Totalf = new SqlCommand("SELECT dbo.Tcupom(@code)", conex1);
    SqlParameter code1 = new SqlParameter("@code", SqlDbType.Int);
    code1.Value = cupom;
    SAIDA = (float)Totalf.ExecuteScalar();

    return SAIDA;
}

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