Set an empty DateTime variable

Question

I would declare an empty String variable like this       string myString   string Empty    Is there an equivalent for a  DateTime  variable    Update    The problem is I use this  DateTime  as a parameter for a  StoredProcedure  in SQL  E g       DateTime  someDate   null      myCommand Parameters AddWithValue   SurgeryDate   someDate     When I run this code an exception is catched telling me the  StoredProcedure  expected a   SurgeryDate  parameter  But i provided it  Any idea why

User · Answer

You may want to use a nullable datetime   Datetime  someDate   null   You may find instances of people using DateTime Max or DateTime Min in such instances  but I highly doubt you want to do that   It leads to bugs with edge cases  code that s harder to read  etc

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Since DateTime is a value type you cannot assign null to it  but exactly for these cases  absence of a value  Nullable lt T gt  was introduced - use a nullable DateTime instead   DateTime  myTime   null

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This will work for null able dateTime parameter           SearchUsingDate DateTime  StartDate  DateTime  EndDate        DateTime LastDate       if  EndDate    null                     LastDate    DateTime EndDate            LastDate   LastDate AddDays 1             EndDate   LastDate

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The  addwithvalue needs dbnull  You could do something like this   DateTime  someDate   null        if  someDate    null      myCommand Parameters AddWithValue   SurgeryDate   DBnull value     or use a method extension       public static class Extensions               public static SqlParameter AddWithNullValue this SqlParameterCollection collection  string parameterName  object value                        if  value    null                  return collection AddWithValue parameterName  DBNull Value               else                 return collection AddWithValue parameterName  value

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Option 1  Use a nullable DateTime   Option 2  Use DateTime MinValue  Personally  I d prefer option 1

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You can set a DateTime variable to be  1 1 0001 00 00 00  but the variable itself cannot be null  To get this MinTime use   DateTime variableName   DateTime MinValue

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A string is a sequence of characters  So it makes sense to have an empty string  which is just an empty sequence of characters   But DateTime is just a single value  so it s doesn t make sense to talk about an    empty    DateTime   If you want to represent the concept of    no value     that s represented as null in  Net  And if you want to use that with value types  you need to explicitly make them nullable  That means either using Nullable lt DateTime gt   or the equivalent DateTime    DateTime  just like all value types  also has a default value  that s assigned to uninitialized fields and you can also get it by new DateTime   or default DateTime   But you probably don t want to use it  since it represents valid date  1 1 0001 0 00 00

User · Answer

No  You have 2 options   DateTime date   DateTime MinValue    This works when you need to do something every X amount of time  since you will always be over MinValue  but can actually cause subtle errors  such as using some operators w o first checking if you are not MinValue  if you are not careful   And you can use Nullable   DateTime  date   null    Which is nice and avoids most issues while introducing only 1 or 2   It really depends on what you are trying to achieve

User · Answer

The method you used  AddWithValue  doesn t convert null values to database nulls  You should use DBNull Value instead   myCommand Parameters AddWithValue        SurgeryDate        someDate    null   DBNull Value    object someDate      This will pass the someDate value if it is not null  or DBNull Value otherwise  In this case correct value will be passed to the database

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Either   DateTime dt   new DateTime      or  DateTime dt   default DateTime

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If you set the date to   DateTime dNewDate   new DateTime      The value is set to  1 1 0001 12 00 00 AM

User · Answer

There s no such thing as an empty date per se  do you mean something like   DateTime  myDateTime   null

[c#] Set an empty DateTime variable

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