Casting a NULL value

Question

I'm trying to populate a class object with values from a database table. The someObject.Property field is a nullable int type.

someObject.Property = Convert.ToInt32(dbReader["SomeField"]);

So, if SomeField is null, Convert will give a DBNull error. Is there a specific method I should be using for this?

Yuck · Accepted Answer · 2011-09-20T11:55:22.367

5

This should work...

someObject.Property = dbReader["SomeField"].Equals(DBNull.Value)
    ? null
    : (Int32)dbReader["SomeField"];

@John - Good catch. Edit to reflect that oversight.

edited Sep 20 '11 at 11:55

answered May 19 '11 at 16:58

Yuck

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-1: DBNull is a type, not a value. You need to compare to `DBNull.Value`. And you'd do better to use `IsDbNull`. – John Saunders May 19 '11 at 17:15

Iain Ward · Answer 2 · 2011-05-25T09:05:25.417

This method may be useful for what you're trying to do. It will try and parse the column value into it's respective type, and if it can't it will the return the types default value.

public T ParseValue<T>(System.Data.SqlClient.SqlDataReader reader, string column)
{
     T result = default(T);
     int index = reader.GetOrdinal(column);
     if (!reader.IsDBNull(index))
         result = (T)reader.GetValue(index);

     return result;
}

score 2 · Answer 3 · answered May 19 '11 at 16:57

2

I use this, replacing 0 with whatever default. If the property is nullable then you would default to the C# null.

someObject.Property = (DBNull.Value.Equals(dbReader["SomeField"])) ? 0 : Convert.ToInt32(dbReader["SomeField"]);

answered May 19 '11 at 16:57

Dustin Laine

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His property is an `Int32?` so probably `null` is preferred. Otherwise same idea. =) – Yuck May 19 '11 at 16:58
Whoops, missed that in your post. He did state "The someObject.Property field is a nullable int type." – Yuck May 19 '11 at 17:01

score 1 · Answer 4 · answered May 19 '11 at 16:58

1

There is TryParse

http://msdn.microsoft.com/en-us/library/f02979c7.aspx

You can also look at using the null coalescing operator ?? to give a default value if needed.

answered May 19 '11 at 16:58

manojlds

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score 1 · Answer 5 · edited May 19 '11 at 16:59

1

You could use TryParse. This won't specifically check for NULLs but it will tell you whether it is parseable or not which is probably what you really want.

bool result = Int32.TryParse(value, out number);

edited May 19 '11 at 16:59

manojlds

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answered May 19 '11 at 16:58

Joe Phillips

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score 0 · Answer 6 · edited Aug 11 '12 at 11:35

0

You can use this:

if (reader["SomeField"] != DBNull.Value)
    someObject.Property = reader.GetInt32(dbReader("SomeField"));

edited Aug 11 '12 at 11:35

Adi Lester

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answered May 19 '11 at 16:58

Akrem

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score 0 · Answer 7 · edited Aug 11 '12 at 11:25

0

int someFieldIndex = reader.GetOrdinal("SomeField");
someObject.Property = reader.IsDbNull(someFieldIndex) ? null : (Int32?)reader.GetInt32(someFieldIndex);

edited Aug 11 '12 at 11:25

Adi Lester

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answered May 19 '11 at 17:00

Nitin Midha

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score 0 · Answer 8 · answered May 19 '11 at 17:12

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someObject.Property = Convert.ToInt32(dbReader["SomeField"].ToString());

answered May 19 '11 at 17:12

Nighil

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Casting a NULL value

8 Answers8