Working with null values in memory.

Question

Int32, bool, float, etc. are all memory structs/value types, and the value of 'null' is a pointer (a zero pointer precisely) therefore it isn't possible to assign null to an struct/value type. This in itself isn't an issue until you throw in a database. The values from the database can be null, what strategies when working with null values in memory from one of the value types? I'm using C# to build a system. Thanks in advance.

eksypnos123 · Answer

To test for null you use DBnull: // set the value of the first column in the row to null row[0] = DBNull.Value; // test the first column to determine if it contains a null value Boolean isNull = (row[0] == DBNull.Value); or: Boolean isNull = row.IsNull(0);

aksingh01in · Answer

i m agree with u

gkj · Answer

Int is not a class, it is a struct, therefore it doesn't have a concept of "Nothing" (VB.Net) or "null" (C#), which is the problem. An interesting solution has come up that is worth considering. In C# you have have operator overloading, so you could create a struct called NullBool in which true, false, and null could be assigned as values, and use operator overloading to internally represent what true, false, and null represented. For you VB'ers, you have to wait until 2005 for operator overloading, but us C#'ers can use it right away.

p.jones · Answer

What stops you testing memory for Nothing? That is .NET speak for null, yes? Memory in .NET is really objects usually, either the object reference is null or the object exists but the particular property/value is null, yes? But then Microsoft uses the term Nothing in place of null.

Carlos Sanchez · Answer

Ok, I guess I understood. I was in the same situation of the case of the termination date. Well, you want to retrieve data from a DataBase and store them in variables. I guess is not posibble. But my doubt is that it's necessary to store them in variables. I mean, is not possible doing the statements from a condition? I guess you want the variables to compare them to another values, something like: if ( boolVariable == true) { //Statement } if ( boolVariable == false) { //Statement } if ( boolVariable == null) { //Not possible //Statement } So, is not possible working directly with the DataBase values? Something like: if ( DR.GetBoolean( ColumnNumber) == true) { //Statement } if ( DR.GetBoolean( ColumnNumber) == false) { //Statement } if ( DR.IsDBNull( ColumnNumber)) { //Now is possible //Statement } I'll be sorry if this is not that you are hoping. If I didn't understand your idea post it plz. Regards!

gkj · Answer

I come from an Oracle Database and PL/SQL background where columns can have a value or be null. If I represent a boolean at the string "T" or "F", then there is no problem understand "T" as true and "F" as false in the software. The question is, what if you have a situation where you don't know the value is either true or false, its unknown. Historically from a database perspective, you'd store a null value to indicate that neither T or F were possible. A better example would be a DateTime field. I might have two dates in a database representing an effective and termination date, where the termination is null until it is known. In this situation there are billions of possible DateTime values, but null (as unknown) is specific. I cannot have a "null" DateTime attribute, so how do I represent the fact that the DateTime is null in the database? I was hoping that there would be a good strategy for handling NULL in memory. In Java, for instance, they have the equivilant of an "int" value type and an "Integer" class. In this case, you can assign NULL to the Integer object and this has a specific testable value, but .Net doesn't seem to have a similar strategy. Right now, I use a data reader to load data from a SQL statement, and assign a default value to the attribute, such as: myOrdinal = DR.GetOrdinal( "TotalDebt" ); if ( DR.IsDBNull( myOrdinal ) ) { myEntity.TotalDebt = 0; } else { myEntity.TotalDebt = DR.GetFloat( myOrdinal ); }//if Where DR is a DataReader and myEntity.TotalDebt is defined as: private float iTotalDebt; public float TotalDebt { get { return iTotalDebt; } set { iTotalDebt = value; } }//TotalDebt Note: I'm not using a DataSet because according to Microsoft's documentation, if I'm going to transcribe the data into an object on my Business tier, the DataSet is very inefficient ... besides, even if the DataSet were able to store a null, it wouldn't solve the problem just postpone it until I constructed my object from the data entity. Thoughts?

Carlos Sanchez · Answer

I guess is not possible that you want. But, if you have a boolean column in your DataBase, why would you want a third value? If you need a third, value may be you need another value type. In the case of the int value, the zero could represents the null value. May be if you post your whole idea we could help you. Regards.

gkj · Answer

In the database, I can store a NULL, but when I am working in memory, the value types; bool, int, DataTime, don't support null. So the question becomes, what is the best way to handle a null in memory? In a database, a boolean value can have three values true, false, and null, where null is unknown. In memory it can only have two values true/false. How do I represent the third unknown value while working with that value in memory?

Carlos Sanchez · Answer

What is your idea? Do u want to assign null to a DataBase?

Working with null values in memory.

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