How to resolve this SqlDataReader "Possible null reference assignment" warning?

Question

I just cannot figure out what is needed to resolve the warning about the possible null reference assignment in the following case:

item.UniqueId = Convert.IsDBNull(reader["UniqueID"]) ? string.Empty : reader["UniqueID"].ToString()

If the field value is NULL, it should set the property to an empty string, otherwise it should set it to the field value converted to a string. The field is defined as PK, varchar(11), not null.

if I define the UniqueID property as string? then the warning goes away, but it cannot be null so I don't want to do that.

I was under the impression that ToString() cannot return a null result.

"ToString() cannot return a null result" - Incorrect. The return type of Object.ToString is String?. — madreflection
– madreflection, Commented Sep 27, 2022 at 22:23
If the field is defined as not null, then when would you ever get a DBNull object? Could you not just do reader["UniqueID"].ToString() ?? string.Empty? — codeMonkey
– codeMonkey, Commented Sep 27, 2022 at 22:32

LarsTech · Accepted Answer · 2022-09-28 20:01:25Z

0

As per @codeMonkey's comment, the warning can be resolved by checking for the null return of the ToString() method.

item.UniqueId = reader["UniqueID"].ToString() ?? string.Empty;

edited Sep 28, 2022 at 20:01

LarsTech

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answered Sep 28, 2022 at 19:58

SiBrit

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Comments

T.S. · Accepted Answer · 2022-09-28 20:15:42Z

0

I don't code like this. I write extensions that I use with my implementations with IDataReader. And this covers all DB providers I use, for example MySqlDatareader, SqlDataReader, OracleDataReader

public static string GetStringValue (this IDataReader r, sting f, string d) // f - field, d - default
{
    if (DBNull.Value.Equals(r[f]) || r[f] == null)
        return d;
    
    return r[f].ToString();
}

Usage

string x = null;
if (reader.Read())
    x = reader.GetStringValue("fieldName", "defaultValue or null");

answered Sep 28, 2022 at 20:15

T.S.

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