Setting the default value of a DateTime Property to DateTime Now inside the System ComponentModel Default Value Attrbute

Question

Does any one know how I can specify the Default value for a DateTime property using the System ComponentModel DefaultValue Attribute   for example I try this    DefaultValue typeof DateTime  DateTime Now ToString  yyyy-MM-dd     public DateTime DateCreated   get  set      And it expects the value to be a constant expression   This is in the context of using with ASP NET Dynamic Data   I do not want to scaffold the DateCreated column but simply supply the DateTime Now if it is not present   I am using the Entity Framework as my Data Layer  Cheers   Andrew

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There s no reason I can come up with that it shouldn t be possible to do through an attribute  It might be in Microsoft s backlog  Who knows   The best solution I have found is to use the defaultValueSql parameter in the code first migration   CreateTable       dbo SomeTable       c   gt  new                       TheDateField   c DateTime defaultValueSql   GETDATE                   I don t like the often reference solution of setting it in the entity class constructor because if anything other than Entity Framework sticks a record in that table  the date field won t get a default value  And the idea of using a trigger to handle that case just seems wrong to me

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A simple solution if you are using the Entity Framework is the add a partical class and define a constructor for the entity as the framework does not define one   For example if you have an entity named Example you would put the following code in a seperate file   namespace EntityExample       public partial class Example   EntityObject               public Example                            Initialize certain default values here              this  DateCreated   DateTime Now

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With EF 7   DatabaseGenerated DatabaseGeneratedOption Identity   Column TypeName    quot datetime2 quot    DateTime  Dateadded   get  set     migration script  AlterColumn  quot myschema mytable quot    quot Dateadded quot   c   gt  c DateTime nullable  false  precision  7  storeType   quot datetime2 quot   defaultValueSql   quot getutcdate   quot      result  ALTER TABLE  MySchema   MyTable  ADD  CONSTRAINT  DF MySchema MyTable Dateadded   DEFAULT  getutcdate    FOR  Dateadded

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I think you can do this using StoreGeneratedPattern   Identity  set in the model designer properties window    I wouldn t have guessed that would be how to do it  but while trying to figure it out I noticed that some of my date columns were already defaulting to CURRENT TIMESTAMP   and some weren t  Checking the model  I see that the only difference between the two columns besides the name is that the one getting the default value has StoreGeneratedPattern set to Identity   I wouldn t have expected that to be the way  but reading the description  it sort of makes sense      Determines if the corresponding column in the database will be auto-generated during insert and update operations    Also  while this does make the database column have a default value of  now   I guess it does not actually set the property to be DateTime Now in the POCO  This hasn t been an issue for me as I have a customized  tt file that already sets all of my date columns to DateTime Now automatically  it s actually not hard to modify the  tt file yourself  especially if you have ReSharper and get a syntax highlighting plugin   Newer versions of VS may already syntax highlight  tt files  not sure     The issue for me was  how do I get the database column to have a default so that existing queries that omit that column will still work  And the above setting worked for that   I haven t tested it yet but it s also possible that setting this will interfere with setting your own explicit value   I only stumbled upon this in the first place because EF6 Database First wrote the model for me this way

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I know this post is a little old  but a have a suggestion that may help some   I used an Enum to determine what to set in the attribute constructor   Property declaration     DbProperty initialValue  EInitialValue DateTime Now   public DateTime CreationDate   get  set      Property constructor    Public Class DbProperty Inherits System Attribute      Public Property InitialValue As Object      Public Sub New ByVal initialValue As EInitialValue         Select Case initialValue           Case EInitialValue DateTime Now              Me InitialValue   System DateTime Now            Case EInitialValue DateTime Min              Me InitialValue   System DateTime MinValue            Case EInitialValue DateTime Max              Me InitialValue   System DateTime MaxValue         End Select      End Sub End Class   Enum    Public Enum EInitialValue    DateTime Now    DateTime Min    DateTime Max End Enum

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I needed a UTC Timestamp as a default value and so modified Daniel s solution like this        Column TypeName    datetime2         XmlAttribute       DisplayFormat ApplyFormatInEditMode   true  DataFormatString     0 yyyy-MM-dd          Display Name    Date Modified         DateRange Min    1900-01-01   Max    2999-12-31        public DateTime DateModified           get   return dateModified            set   dateModified   value               private DateTime dateModified   DateTime Now ToUniversalTime      For DateRangeAttribute tutorial  see this awesome blog post

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public DateTime DateCreated      get            return  this dateCreated    default DateTime              this dateCreated   DateTime Now            this dateCreated           set   this dateCreated   value      private DateTime dateCreated   default DateTime

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There is a way  Add these classes    DefaultDateTimeValueAttribute cs  using System  using System ComponentModel  using System ComponentModel DataAnnotations  using System Linq  using System Reflection  using System Runtime CompilerServices  using Custom Extensions   namespace Custom DefaultValueAttributes            lt summary gt          This class s DefaultValue attribute allows the programmer to use DateTime Now as a default value for a property          Inspired from https   code msdn microsoft com A-flexible-Default-Value-11c2db19            lt  summary gt       AttributeUsage AttributeTargets Property       public sealed class DefaultDateTimeValueAttribute   DefaultValueAttribute               public string DefaultValue   get  set            private object  value           public override object Value                       get                               if   value    null                      return  value   GetDefaultValue                     return  value                                        lt summary gt              Initialized a new instance of this class using the desired DateTime value  A string is expected  because the value must be generated at runtime              Example of value to pass  Now  This will return the current date and time as a default value               Programmer tip  Even if the parameter is passed to the base class  it is not used at all  The property Value is overridden               lt  summary gt               lt param name  defaultValue  gt Default value to render from an instance of  lt see cref  DateTime   gt  lt  param gt          public DefaultDateTimeValueAttribute string defaultValue    base defaultValue                        DefaultValue   defaultValue                     public static DateTime GetDefaultValue Type objectType  string propertyName                        var property   objectType GetProperty propertyName               var attribute   property GetCustomAttributes typeof DefaultDateTimeValueAttribute   false                    Cast lt DefaultDateTimeValueAttribute gt                      FirstOrDefault                 return attribute GetDefaultValue                       private DateTime GetDefaultValue                            Resolve a named property of DateTime  like  Now              if  this IsProperty                                return GetPropertyValue                                  Resolve a named extension method of DateTime  like  LastOfMonth              if  this IsExtensionMethod                                return GetExtensionMethodValue                                  Parse a relative date             if  this IsRelativeValue                                return GetRelativeValue                                  Parse an absolute date             return GetAbsoluteValue                       private bool IsProperty               gt  typeof DateTime  GetProperties                    Select p   gt  p Name  Contains this DefaultValue            private bool IsExtensionMethod               gt  typeof DefaultDateTimeValueAttribute  Assembly                  GetType typeof DefaultDateTimeExtensions  FullName                   GetMethods                    Where m   gt  m IsDefined typeof ExtensionAttribute   false                    Select p   gt  p Name  Contains this DefaultValue            private bool IsRelativeValue               gt  this DefaultValue Contains                private DateTime GetPropertyValue                         var instance   Activator CreateInstance lt DateTime gt                 var value    DateTime instance GetType                    GetProperty this DefaultValue                   GetValue instance                return value                     private DateTime GetExtensionMethodValue                         var instance   Activator CreateInstance lt DateTime gt                 var value    DateTime typeof DefaultDateTimeValueAttribute  Assembly                  GetType typeof DefaultDateTimeExtensions  FullName                   GetMethod this DefaultValue                   Invoke instance  new object     DateTime Now                  return value                     private DateTime GetRelativeValue                         TimeSpan timeSpan              if   TimeSpan TryParse this DefaultValue  out timeSpan                                 return default DateTime                              return DateTime Now Add timeSpan                      private DateTime GetAbsoluteValue                         DateTime value              if   DateTime TryParse this DefaultValue  out value                                 return default DateTime                              return value                      DefaultDateTimeExtensions cs  using System   namespace Custom Extensions            lt summary gt          Inspired from https   code msdn microsoft com A-flexible-Default-Value-11c2db19  See usage for more information           lt  summary gt      public static class DefaultDateTimeExtensions               public static DateTime FirstOfYear this DateTime dateTime                gt  new DateTime dateTime Year  1  1  dateTime Hour  dateTime Minute  dateTime Second  dateTime Millisecond            public static DateTime LastOfYear this DateTime dateTime                gt  new DateTime dateTime Year  12  31  dateTime Hour  dateTime Minute  dateTime Second  dateTime Millisecond            public static DateTime FirstOfMonth this DateTime dateTime                gt  new DateTime dateTime Year  dateTime Month  1  dateTime Hour  dateTime Minute  dateTime Second  dateTime Millisecond            public static DateTime LastOfMonth this DateTime dateTime                gt  new DateTime dateTime Year  dateTime Month  DateTime DaysInMonth dateTime Year  dateTime Month   dateTime Hour  dateTime Minute  dateTime Second  dateTime Millisecond             And use DefaultDateTimeValue as an attribute to your properties  Value to input to your validation attribute are things like  Now   which will be rendered at run time from a DateTime instance created with an Activator  The source code is inspired from this thread  https   code msdn microsoft com A-flexible-Default-Value-11c2db19  I changed it to make my class inherit with DefaultValueAttribute instead of a ValidationAttribute

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How you deal with this at the moment depends on what model you are using Linq to SQL or EntityFramework   In L2S you can add   public partial class NWDataContext       partial void InsertCategory Category instance                if Instance Date    null              Instance Data   DateTime Now           ExecuteDynamicInsert instance             EF is a little more complicated see http   msdn microsoft com en-us library cc716714 aspx for more info on EF buisiness logic

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I have tested this on EF core 2 1  Here you cannot use either Conventions or Data Annotations  You must use the Fluent API   class MyContext   DbContext       public DbSet lt Blog gt  Blogs   get  set         protected override void OnModelCreating ModelBuilder modelBuilder                modelBuilder Entity lt Blog gt                 Property b   gt  b Created               HasDefaultValueSql  getdate                Official doc

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It is possible and quite simple   for DateTime MinValue   System ComponentModel DefaultValue typeof DateTime          for any other value as last argument of DefaultValueAttribute specify string that represent desired DateTime value   This value must be constant expression and is required to create object  DateTime  using TypeConverter

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I also wanted this and came up with this solution  I m only using the date part - a default time makes no sense as a PropertyGrid default    public class DefaultDateAttribute   DefaultValueAttribute     public DefaultDateAttribute short yearoffset        base DateTime Now AddYears yearoffset  Date            This just creates a new attribute that you can add to your DateTime property  E g  if it defaults to DateTime Now Date    DefaultDate 0

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I faced the same issue  but the one which works for me best is below   public DateTime CreatedOn   get  set      DateTime Now

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I think the easiest solution is to set  Created DATETIME2 NOT NULL DEFAULT GETDATE     in column declaration and in VS2010 EntityModel designer set corresponding column property StoreGeneratedPattern   Computed

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using System ComponentModel DataAnnotations Schema    DatabaseGenerated DatabaseGeneratedOption Computed   public DateTime CreatedOn   get  private set

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Simply consider setting its value in the constructor of your entity class  public class Foo          public DateTime DateCreated   get  set           public Foo                       DateCreated   DateTime Now

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You cannot do this with an attribute because they are just meta information generated at compile time  Just add code to the constructor to initialize the date if required  create a trigger and handle missing values in the database  or implement the getter in a way that it returns DateTime Now if the backing field is not initialized   public DateTime DateCreated      get            return this dateCreated HasValue            this dateCreated Value            DateTime Now           set   this dateCreated   value       private DateTime  dateCreated   null

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In C  Version 6 it s possible to provide a default value  public DateTime fieldname   get  set      DateTime Now

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Creating a new attribute class is a good suggestion  In my case  I wanted to specify  default DateTime   or  DateTime MinValue  so that the Newtonsoft Json serializer would ignore DateTime members without real values    JsonProperty  DefaultValueHandling   DefaultValueHandling Ignore     DefaultDateTime  public DateTime EndTime   public class DefaultDateTimeAttribute   DefaultValueAttribute       public DefaultDateTimeAttribute             base  default  DateTime              public DefaultDateTimeAttribute  string dateTime             base  DateTime Parse  dateTime             Without the DefaultValue attribute  the JSON serializer would output  1 1 0001 12 00 00 AM  even though the DefaultValueHandling Ignore option was set

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Just found this looking for something different  but in the new C  version  you can use an even shorter version for that   public DateTime DateCreated   get  set      DateTime Now

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Add below to the DateTime property   DatabaseGenerated DatabaseGeneratedOption Computed

[c#] Setting the default value of a DateTime Property to DateTime.Now inside the System.ComponentModel Default Value Attrbute

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