Entity Framework 6 Code first Default value

Question

is there  elegant  way to give specific property a default value    Maybe by DataAnnotations  something like     DefaultValue  true    public bool Active   get  set      Thank you

User · Answer

It s simple  Just annotate with required    Required  public bool MyField   get  set      the resultant migration will be   migrationBuilder AddColumn lt bool gt   name   MyField   table   MyTable   nullable  false  defaultValue  false     If you want true  change the defaultValue to true in the migration before updating the database

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Just Overload the default constructor of Model class and pass any relevant parameter which you may or may not use  By this you can easily supply default values for attributes  Below is an example   using System  using System Collections Generic  using System ComponentModel  using System ComponentModel DataAnnotations  using System Linq  using System Text  using System Threading Tasks   namespace Aim Data Domain        MetadataType typeof LoginModel        public partial class Login                      public Login bool status                        this CreatedDate   DateTime Now              this ModifiedDate   DateTime Now              this Culture    EN-US               this IsDefaultPassword   status              this IsActive   status              this LoginLogs   new HashSet lt LoginLog gt                 this LoginLogHistories   new HashSet lt LoginLogHistory gt                            public class LoginModel                 Key           ScaffoldColumn false            public int Id   get  set             Required          public string LoginCode   get  set             Required          public string Password   get  set            public string LastPassword   get  set                 public int UserGroupId   get  set            public int FalseAttempt   get  set            public bool IsLocked   get  set            public int CreatedBy   get  set                   public System DateTime CreatedDate   get  set            public Nullable lt int gt  ModifiedBy   get  set                  public Nullable lt System DateTime gt  ModifiedDate   get  set                   public string Culture   get  set                    public virtual ICollection lt LoginLog gt  LoginLogs   get  set            public virtual ICollection lt LoginLogHistory gt  LoginLogHistories   get  set

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I admit that my approach escapes the whole  Code First  concept  But if you have the ability to just change the default value in the table itself    it s much simpler than the lengths that you have to go through above    I m just too lazy to do all that work    It almost seems as if the posters original idea would work    DefaultValue true   public bool IsAdmin   get  set      I thought they just made the mistake of adding quotes    but alas no such intuitiveness  The other suggestions were just too much for me  granted I have the privileges needed to go into the table and make the changes    where not every developer will in every situation   In the end I just did it the old fashioned way  I set the default value in the SQL Server table    I mean really  enough already  NOTE  I further tested doing an add-migration and update-database and the changes stuck

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You can do it by manually edit code first migration   public override void Up            AddColumn  dbo Events    Active   c   gt  c Boolean nullable  false  defaultValue  true

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In  NET Core 3 1 you can do the following in the model class       public bool  Active   get  set       In the DbContext OnModelCreating you add the default value       protected override void OnModelCreating ModelBuilder modelBuilder                modelBuilder Entity lt Foundation gt                 Property b   gt  b Active               HasDefaultValueSql  1             base OnModelCreating modelBuilder           Resulting in the following in the database    Note  If you don t have nullable  bool   for you property you will get the following warning  The  bool  property  Active  on entity type  Foundation  is configured with a database-generated default  This default will always be used for inserts when the property has the value  false   since this is the CLR default for the  bool  type  Consider using the nullable  bool   type instead so that the default will only be used for inserts when the property value is  null

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The above answers really helped  but only delivered part of the solution  The major issue is that as soon as you remove the Default value attribute  the constraint on the column in database won t be removed  So previous default value will still stay in the database  Here is a full solution to the problem  including removal of SQL constraints on attribute removal  I am also re-using  NET Framework s native DefaultValue attribute  Usage  DatabaseGenerated DatabaseGeneratedOption Computed    DefaultValue  quot getutcdate   quot    public DateTime CreatedOn   get  set     For this to work you need to update IdentityModels cs and Configuration cs files IdentityModels cs file Add update this method in your ApplicationDbContext class protected override void OnModelCreating DbModelBuilder modelBuilder                base OnModelCreating modelBuilder               var convention   new AttributeToColumnAnnotationConvention lt DefaultValueAttribute  string gt   quot SqlDefaultValue quot    p  attributes    gt  attributes SingleOrDefault   Value ToString                 modelBuilder Conventions Add convention      Configuration cs file Update your Configuration class constructor by registering custom Sql generator  like this  internal sealed class Configuration   DbMigrationsConfiguration lt ApplicationDbContext gt        public Configuration                    DefaultValue Sql Generator         SetSqlGenerator  quot System Data SqlClient quot   new DefaultValueSqlServerMigrationSqlGenerator              Next  add custom Sql generator class  you can add it to the Configuration cs file or a separate file  internal class DefaultValueSqlServerMigrationSqlGenerator   SqlServerMigrationSqlGenerator       private int dropConstraintCount       protected override void Generate AddColumnOperation addColumnOperation                SetAnnotatedColumn addColumnOperation Column  addColumnOperation Table           base Generate addColumnOperation              protected override void Generate AlterColumnOperation alterColumnOperation                SetAnnotatedColumn alterColumnOperation Column  alterColumnOperation Table           base Generate alterColumnOperation              protected override void Generate CreateTableOperation createTableOperation                SetAnnotatedColumns createTableOperation Columns  createTableOperation Name           base Generate createTableOperation              protected override void Generate AlterTableOperation alterTableOperation                SetAnnotatedColumns alterTableOperation Columns  alterTableOperation Name           base Generate alterTableOperation              private void SetAnnotatedColumn ColumnModel column  string tableName                if  column Annotations TryGetValue  quot SqlDefaultValue quot   out var values                         if  values NewValue    null                                column DefaultValueSql   null                  using var writer   Writer                        Drop Constraint                 writer WriteLine GetSqlDropConstraintQuery tableName  column Name                    Statement writer                             else                               column DefaultValueSql    string values NewValue                                     private void SetAnnotatedColumns IEnumerable lt ColumnModel gt  columns  string tableName                foreach  var column in columns                        SetAnnotatedColumn column  tableName                        private string GetSqlDropConstraintQuery string tableName  string columnName                var tableNameSplitByDot   tableName Split               var tableSchema   tableNameSplitByDot 0           var tablePureName   tableNameSplitByDot 1            var str      quot DECLARE  var dropConstraintCount  nvarchar 128  SELECT  var dropConstraintCount    name FROM sys default constraints WHERE parent object id   object id N  tableSchema    tablePureName     AND col name parent object id  parent column id      columnName    IF  var dropConstraintCount  IS NOT NULL EXECUTE  ALTER TABLE  tableSchema    tablePureName   DROP CONSTRAINT       var dropConstraintCount         quot            dropConstraintCount            return str

User · Answer

Set the default value for the column in table in MSSQL Server  and in class code add attribute  like this    DatabaseGenerated DatabaseGeneratedOption Computed     for the same property

User · Answer

In EF core released 27th June 2016 you can use fluent API for setting default value  Go to ApplicationDbContext class  find create the method name OnModelCreating and add the following fluent API   protected override void OnModelCreating ModelBuilder modelBuilder    modelBuilder Entity lt YourTableName gt             Property b   gt  b Active           HasDefaultValue true

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I found that just using Auto-Property Initializer on entity property is enough to get the job done   For example    public class Thing       public bool IsBigThing  get  set      false

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Hmm    I do DB first  and in that case  this is actually a lot easier  EF6 right  Just open your model  right click on the column you want to set a default for  choose properties  and you will see a  DefaultValue  field   Just fill that out and save   It will set up the code for you   Your mileage may vary on code first though  I haven t worked with that   The problem with a lot of other solutions  is that while they may work initially  as soon as you rebuild the model  it will throw out any custom code you inserted into the machine-generated file   This method works by adding an extra property to the edmx file    lt EntityType Name  Thingy  gt     lt Property Name  Iteration  Type  Int32  Nullable  false    DefaultValue  1      gt    And by adding the necessary code to the constructor   public Thingy       this Iteration   1

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After  SedatKapanoglu comment  I am adding all my approach that works  because he was right  just using the fluent API does not work   1- Create custom code generator and override Generate for a ColumnModel      public class ExtendedMigrationCodeGenerator   CSharpMigrationCodeGenerator        protected override void Generate ColumnModel column  IndentedTextWriter writer  bool emitName   false                 if  column Annotations Keys Contains  Default                          var value   Convert ChangeType column Annotations  Default   NewValue  column ClrDefaultValue GetType                 column DefaultValue   value                      base Generate column  writer  emitName              2- Assign the new code generator   public sealed class Configuration   DbMigrationsConfiguration lt Data Context EfSqlDbContext gt        public Configuration                 CodeGenerator   new ExtendedMigrationCodeGenerator            AutomaticMigrationsEnabled   false            3- Use fluent api to created the Annotation   public static void Configure DbModelBuilder builder       builder Entity lt Company gt    Property c   gt  c Status  HasColumnAnnotation  Default   0

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Lets consider you have a class name named Products and you have a IsActive field  just you need a create constructor    Public class Products       public Products                IsActive   true         public string Field1   get  set     public string Field2   get  set     public bool IsActive   get  set        Then your IsActive default value is True    Edite    if you want to do this with SQL use this command    protected override void OnModelCreating ModelBuilder modelBuilder        modelBuilder Entity lt Blog gt             Property b   gt  b IsActive           HasDefaultValueSql  true

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Your model properties don t have to be  auto properties  Even though that is easier  And the DefaultValue attribute is really only informative metadata The answer accepted here is one alternative to the constructor approach   public class Track        private const int DEFAULT LENGTH   400      private int  length   DEFAULT LENGTH       DefaultValue DEFAULT LENGTH       public int LengthInMeters           get   return  length            set    length   value              vs   public class Track       public Track                 LengthInMeters   400                public int LengthInMeters   get  set                This will only work for applications creating and consuming data using this specific class  Usually this isn t a problem if data access code is centralized  To update the value across all applications you need to configure the datasource to set a default value  Devi s answer shows how it can be done using migrations  sql  or whatever language your data source speaks

User · Answer

What I did  I initialized values in the constructor of the entity  Note  DefaultValue attributes won t set the values of your properties automatically  you have to do it yourself

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It s been a while  but leaving a note for others  I achieved what is needed with an attribute and I decorated my model class fields with that attribute as I want    SqlDefaultValue DefaultValue    getutcdate      public DateTime CreatedDateUtc   get  set      Got the help of these 2 articles    EF on CodePlex Andy Mehalick blog   What I did   Define Attribute   AttributeUsage AttributeTargets Property  AllowMultiple   false   public class SqlDefaultValueAttribute   Attribute       public string DefaultValue   get  set        In the  OnModelCreating  of the context  modelBuilder Conventions Add  new AttributeToColumnAnnotationConvention lt SqlDefaultValueAttribute  string gt   SqlDefaultValue    p  attributes    gt  attributes Single   DefaultValue      In the custom SqlGenerator  private void SetAnnotatedColumn ColumnModel col        AnnotationValues values      if  col Annotations TryGetValue  SqlDefaultValue   out values                  col DefaultValueSql    string values NewValue            Then in the Migration Configuration constructor  register the custom SQL generator   SetSqlGenerator  System Data SqlClient   new CustomMigrationSqlGenerator

[entity-framework] Entity Framework 6 Code first Default value

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