I am adding new extension method for checking null value for any object on following criteria:
Should return true if value for class object is null
Should return true if object is of type string and having value null or Empty
Should return true if object is of type DateTime and having Min value.
Any other condition for null need to check.(Please suggest if required.)
Here is IsNull() extention method:
public static bool IsNull(this object obj)
{
if (obj == null || obj == DBNull.Value)
return true;
if (obj.GetType() == typeof(string))
return string.IsNullOrEmpty(obj.ToString());
if (obj.GetType() == typeof(DateTime))
{
DateTime _dateValue = DateTime.MinValue;
if (DateTime.TryParse(obj.ToString(), out _dateValue) && _dateValue == DateTime.MinValue)
return true;
}
return false;
}
Now my question is:
Do I need to add check differently for Value and Reference type
object?
Does this extension method handle all type of null check for any
object?
Any suggestion or improvement need to add in extension?
Do I need to add check differenty for Value and Reference type object?
Value types can not be null.
Does this externtion method handle all type of null check for any object?
It looks like (except value types)
Any suggestion or improvement need to add in extention?
As I said value types cannot be null, so you can add an extra condition to check whether the type is value type or not,if so you can return false
if(obj.GetType().IsValueType) return false;
By the way if you write this before the DateTime check,your DateTime condition will become unreachable.It doesn't make sense anyway but it's your choice.If you want to return true when the value equals to DateTime.MinValue it's completely up to you.
A few observations:
1) A value type will never be null. When called on a value type.. it will be boxed to an object.. and won't be null (unless you wrap it in a Nullable<T>).
2) Your method no longer checks for null.. it also checks for a minimum value and empty strings. An empty string is not null - its an empty value. A minimum value is not null.. its a value. It has too much responsibility here and should be renamed.
3) Given what I've said above.. you could just simply do this instead of writing your own function:
if (variable == default(variable.GetType()))
Since that checks for the default of all types.. value types such as DateTime, int, and classes for null. Then, your only other specific check is for DBNull.Value.
Related
I have this code:
messageDto = new CorrelationDto()
{
timestamp = default,
};
var isDefault = messageDto.GetType().GetProperty("timestamp").GetValue(messageDto) == default; // FALSE
var isDefault2 = messageDto.timestamp == default; // TRUE
where timestamp is a DateTime.
As you can see, getting the value through reflection and comparing to default return false. Do you have any idea why it's happening and how should I do to check for default values?
Thanks
== EDIT ==
It has been pointed to me that the return value of GetValue() is an object and so it must be casted to DateTime in order for the default to work. Unfortunately I cannot because I'm running this test on all the properties of an object to discover if this object is initialized or not (so I check for null or default value). And the messageDto in reality is a generic type so I don't know the types of its properties a priori.
GetValue returns an object of type object, because it can't know at compile time what the type of the property is. The default value of an object is null, but since DateTime is a value type, its default value cannot be null.
Cast the result of GetValue to DateTime.
If I correctly understood you, this is how I solved this problem:
private static bool IsValueNumericDefault(object value)
{
var intVal = 1;
var doubleVal = 1.0;
return (int.TryParse($"{value}", out intVal) || double.TryParse($"{value}", out doubleVal)) &&
(intVal == default || doubleVal == default);
}
I check random object value through casting it to string and try parse to type that I check. Value parameter is returned by reflection method .GetValue(). You can try to parse it to DateTime or any other type that you check.
In order to validate if model comes null or not I use something like this:
if (model is null || !model.Any()) return this;
But in latest Microsoft conference I saw guys use something like:
if(model is { })
I try to use it but always return true (if object comes null or not)
So my question is. Is there a new way to check if a model comes null?
What is the correct usage of brackets { }
Note: I googled about that brackets but I found anything. Regards
You can do a generic extension method to check if your object is null or not.
Try:
public static bool IsNullOrEmpty<T>(this IEnumerable<T> source) {
return source?.Any() != true;
}
Another way to check for NullOrEmpty is to coerce Count() to an int?. Then we can compare the result of GetValueOrDefault to 0:
if((model?.Count).GetValueOrDefault() == 0) return this;
How it works:
Because the ?. operator will return null if the left side is null, and Count returns an int, the result of (model?.Count) is a Nullable<int>.
The GetValueOrDefault method returns the value of Count if model is not null, otherwise it returns default(int) (which is 0).
This way if model is null, the condition returns 0
I am trying to read nullable values from a database. Right now my code is converting null values to false. How can I modify my code to allow for null values?
Ap1ExamTaken = dr["AP1_ExamTaken"] != DBNull.Value && Convert.ToBoolean(dr["AP1_ExamTaken"]),
I would like values that are null to be shown as null and not false.
You could use the conditional operator here, to set it to null if the value is DBNull.Value, or a non-nullable value otherwise:
Ap1ExamTaken = dr["AP1_ExamTaken"] == DBNull.Value ? null : (bool?) dr["AP1_ExamTaken"];
Note that this will throw an exception if dr["AP1_ExamTaken"] is a non-boolean, non-DBNull type, which I suspect is what you want.
You could write it more compactly as:
Ap1ExamTaken = dr["AP1_ExamTaken"] as bool?
... but then you'll end up with a null value if the value is some other type (a string, an integer etc) which I'd generally be alarmed about. (If my data doesn't have the shape I expect, I want to know ASAP.)
I want to check the following field in the datatable against null :
r.Field<int>("prod_type")
if (r.Field<int>("prod_type") != null &&
!string.IsNullOrEmpty(r.Field<int>("prod_type").ToString()))
but I get the following exception :
Specified cast is not valid.
How to check the integer value in the datatable against null or empty ?
The Field extension method supports nullable types. Use HasValue to check if a nullable is not null:
if (r.Field<int?>("prod_type").HasValue)
The error you are getting is indicating that the field in the datatable is not of type int. If it is of type int it can't hold null value, instead you can try int? which is Nullable.
r.Field<int?>("prod_type") != null
If prod_type is indeed an int field in the database, try doing it like this:
if (r.Field<int?>("prod_type") != null)
I've got an object, specifically the following:
table.ExtendedProperties["MS_Description"].Value
If there is not property, the Value is null. If there is a property, but it is empty, the Value.toString() is "".
I would thus like to create an if-statement which caters for both eventualities. This is what I've done so far:
if (table.ExtendedProperties["MS_Description"] == null ||
table.ExtendedProperties["MS_Description"].Value.ToString().Equals(""))
The problem is that if it is null, it is still checking the condition on the right-hand-side.
Any ideas?
You can do:
if (table.ExtendedProperties["MS_Description"] == null || string.IsNullOrEmpty(table.ExtendedProperties["MS_Description"].Value))
The reason your code errors is because you don't check if table.ExtendedProperties["MS_Description"].Value is null.
Thus Value is not a string, then you have to deal with all conditions:
var description = table.ExtendedProperties["MS_Description"];
if (description == null ||
description.Value == null ||
description.Value.ToString().Equals(""))
// no value
BTW your code is not quite correct
if (table.ExtendedProperties["MS_Description"] == null ||
table.ExtendedProperties["MS_Description"].Value.ToString().Equals(""))
Instead of checking Value for null, you are checking if table.ExtendedProperties["MS_Description"] is not null. Thats true. You go further, but if table.ExtendedProperties["MS_Description"].Value is null (you didn't check that, remember?), you will get NullReferenceException on applying ToString().
I'm not sure if you are referring to the DataTable.ExtendedProperties property or something else, but if you are, the property returns a System.Data.PropertyCollection, which inherits from System.Collections.HashTable.
Most of the methods and properties, including the indexer ("Item") being discussed here, are directly inherited from HashTable, so in general, table.ExtendedProperties[key] can return any object, including null.
Note that you can also call DataTable.ExtendedProperties.ContainsKey(object key) to determine if the PropertyCollection contains a specific key or not.
Do you know what type of object you are retrieving when you call table.ExtendedProperties["MS_Description"].Value ?
If so, there might be other properties you can use to determine whether the property has been set, etc.
Depending on what type of object table.ExtendedProperties["MS_Description"] is, you might even be able to do something like this:
if ((table.ExtendedProperties["MS_Description"] ?? "").ToString().Length == 0) {
.....
}
That would take into account all of the possibilities:
the key doesn't exist
the key exists, but the value is null
the key exists and the value is empty
as long as the table.ExtendedProperties["MS_Decription"] object returns "" when its Value property is either null or empty.
So a little more information on the object that is returned could go a long way!
string.IsNullOrEmpty(table.ExtendedProperties["MS_Description"].Value)
It looks like table.ExtendedProperties["MS_Description"] is never null, you should be null checking the Value property instead
string value = table.ExtendedProperties["MS_Description"].Value;
if (value == null || value.ToString().Equals(""))
// OR
if (String.IsNullOrEmpty(value))
If table.ExtendedProperties["MS_Description"] can return null, then you need
if (table.ExtendedProperties["MS_Description"] == null ||
String.IsNullOrEmpty(table.ExtendedProperties["MS_Description"].Value.ToString() )
And since table.ExtendedProperties["MS_Description"].Value may return null, then you need
if (table.ExtendedProperties["MS_Description"] == null ||
table.ExtendedProperties["MS_Description"].Value == null ||
String.IsNullOrEmpty(table.ExtendedProperties["MS_Description"].Value.ToString() )