I am using value objects as identities and would like to know how to best deal with nulls in EF core.
For example if I have an employee with an optional title (mr, mrs, etc):
public class Employee
: Entity,
IAggregateRoot
{
public EmployeeTitleId TitleId { get; private set; }
public EmployeeFirstName FirstName { get; private set; }
public EmployeeSurname Surname { get; private set; }
...
}
I could check for nulls everywhere in my code e.g.
if (employee.TitleId == null) ...
or I could use a default e.g.
if (employee.TitleId.Equals(EmployeeTitleId.None)) ...
with the EmployeeTitleId implemented as follows:
public class EmployeeTitleId
: Value<EmployeeTitleId>
{
public static readonly EmployeeTitleId None = new EmployeeTitleId();
protected EmployeeTitleId() { }
public EmployeeTitleId(Guid value)
{
if (value == default)
throw new ArgumentNullException(nameof(value), "Employee title id cannot be empty");
Value = value;
}
public Guid Value { get; internal set; }
public static implicit operator Guid(EmployeeTitleId self) => self.Value;
public static implicit operator EmployeeTitleId(string value)
=> new EmployeeTitleId(Guid.Parse(value));
public override string ToString() => Value.ToString();
}
I would prefer the second approach as it seems cleaner but I don't know if this is overkill. It would also require a bit more setup on the entity framework side e.g.:
builder.OwnsOne(_ => _.TitleId).Property(_ => _.Value)
.HasColumnName("TitleId").HasConversion(v => v == default ? (Guid?) null : v, v => v ?? EmployeeTitleId.None);
Does this seem like a viable approach or should I just stick to checking for null? If so, is there a convention I could use in the entity type configurations so that I don't have to manually set each HasConversion?
There is another way to filter the results globally. You can configure this in the OnModelCreating like:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
// code omitted for brevity
modelBuilder.Entity<Employee>().HasQueryFilter(p => p.TitleId == null);
}
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.
You can do it by manually edit code first migration:
public override void Up()
{
AddColumn("dbo.Events", "Active", c => c.Boolean(nullable: false, defaultValue: true));
}
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<SqlDefaultValueAttribute, string>("SqlDefaultValue", (p, attributes) => 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());
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("getutcdate()")]
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<DefaultValueAttribute, string>("SqlDefaultValue", (p, attributes) => 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<ApplicationDbContext>
{
public Configuration()
{
// DefaultValue Sql Generator
SetSqlGenerator("System.Data.SqlClient", 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("SqlDefaultValue", 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<ColumnModel> 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 = $#"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} + ']')";
dropConstraintCount++;
return str;
}
}
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.
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
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.
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<Data.Context.EfSqlDbContext>
{
public Configuration()
{
CodeGenerator = new ExtendedMigrationCodeGenerator();
AutomaticMigrationsEnabled = false;
}
}
3- Use fluent api to created the Annotation:
public static void Configure(DbModelBuilder builder){
builder.Entity<Company>().Property(c => c.Status).HasColumnAnnotation("Default", 0);
}
It's simple! Just annotate with required.
[Required]
public bool MyField { get; set; }
the resultant migration will be:
migrationBuilder.AddColumn<bool>(
name: "MyField",
table: "MyTable",
nullable: false,
defaultValue: false);
If you want true, change the defaultValue to true in the migration before updating the database
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<Foundation>()
.Property(b => 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'.
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;
}
using System.ComponentModel;
[DefaultValue(true)]
public bool Active { get; set; }
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<YourTableName>()
.Property(b => b.Active)
.HasDefaultValue(true);
}
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<LoginLog>();
this.LoginLogHistories = new HashSet<LoginLogHistory>();
}
}
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<int> ModifiedBy { get; set; }
public Nullable<System.DateTime> ModifiedDate { get; set; }
public string Culture { get; set; }
public virtual ICollection<LoginLog> LoginLogs { get; set; }
public virtual ICollection<LoginLogHistory> LoginLogHistories { get; set; }
}
}
Even from .NET Core 1.0, It is possible to set default values when you are using the code first approach. See the following code snippet.
using System.ComponentModel;
[DefaultValue(true)]
public bool Active { get; set; }
Read for more: Microsoft official docs
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<Blog>()
.Property(b => b.IsActive)
.HasDefaultValueSql("true");
}
The Entity Framework Core Fluent API HasDefaultValue method is used to specify the default value for a database column mapped to a property. The value must be a constant.
public class Contact
{
public int ContactId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Email { get; set; }
public bool IsActive { get; set; }
public DateTime DateCreated { get; set; }
}
public clas SampleContext : DbContext
{
public DbSet<Contact> Contacts { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Context>()
.Propery(p => p.IsActive)
.HasDefaultValue(true);
}
}
Or
like it!
You can also specify a SQL fragment that is used to calculate the default value:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Blog>()
.Property(b => b.Created)
.HasDefaultValueSql("getdate()");
}
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:
<EntityType Name="Thingy">
<Property Name="Iteration" Type="Int32" Nullable="false" **DefaultValue="1"** />
And by adding the necessary code to the constructor:
public Thingy()
{
this.Iteration = 1;
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.
I want to retrieve an object plus its filtered/ordered collection property using EF 5. However, my current code throws an exception:
The Include path expression must refer to a navigation property
defined on the type. Use dotted paths for reference navigation
properties and the Select operator for collection navigation
properties
Here is the class of the object I want to retrieve:
public class EntryCollection
{
[Key]
public int Id { get; set; }
public ICollection<Entry> Entries { get; set; }
...
}
And here is the definition of Entry:
public class Entry
{
[Key]
public int Id { get; set; }
public DateTime Added { get; set; }
...
}
I wanted to retrieve the EntryCollection which contains only the most recent entries, so here is the code I tried:
using (var db = new MyContext())
{
return db.EntryCollections
.Include(ec => ec.Entries.OrderByDescending(e => e.Added).Take(5))
.SingleOrDefault(ec => ec.Foo == "bar');
}
Any ideas?
You cant use OrderBy inside an include.
what about the following
using (var db = new MyContext())
{
return db.EntryCollections
.Where(ec => ec.Foo == "bar")
.Select(ec=> new Something{Entries = ec.Entries.OrderByDescending(e => e.Added).Take(5) }, /*some other properties*/)
.SingleOrDefault();
}
or do it in two seperate queries
I would like to use SQL Server xml type as a column type for an entity class.
According to this thread it's possible to map such a column to string type:
public class XmlEntity
{
public int Id { get; set; }
[Column(TypeName="xml")]
public string XmlValue { get; set; }
}
The table is correctly generated in the datebase by this definition. New XmlEntity objects are also can be created.
But then I try to get some entity from the database:
var entity = db.XmlEntities.Where(e => e.Id == 1).FirstOrDefault();
An error occurs:
One or more validation errors were detected during model generation
System.Data.Edm.EdmEntityType: EntityType 'XElement' has no key defined. Define the key for this EntityType.
The problem was with my wrapper property:
[NotMapped]
public XElement XmlValueWrapper
{
get { return XElement.Parse(XmlValue); }
set { XmlValue = value.ToString(); }
}
I didn't specified NotMapped attribute.
Just to be complete. Here's all code needed, in one part.
[Column(TypeName = "xml")]
public String XmlContent { get; set; }
[NotMapped]
public XElement InitializedXmlContent
{
get { return XElement.Parse(XmlContent); }
set { XmlContent = value.ToString(); }
}
This's how you do that in Data Annotations, if you want to use Fluent API (and use a mapping class) then:
public partial class XmlEntityMap : EntityTypeConfiguration<XmlEntity>
{
public FilterMap()
{
// ...
this.Property(c => c.XmlContent).HasColumnType("xml");
this.Ignore(c => c.XmlValueWrapper);
}
}
If you use Fluent API by overriding OnModelCreating on DbContext then just change those "this" with modelBuilder.Entity<XmlEntity>()
I'm working on a medical application where a grid needs to display the ICD description as well as its associated HCC category description. The ICD and HCC types look like this:
public class ICD {
public String Code { get; set; }
public String Description { get; set; }
public HCC HCC { get; set; }
}
public class HCC {
public Int32 ID { get; set; }
public String Description { get; set; }
}
When I bind the Telerik MVC extensions grid to a list of ICD objects, I'm setting up the columns like so:
this.Html.Telerik().Grid(this.Model.ICDs)
.Name("ICDGrid")
.DataKeys(keys => keys.Add(icd => icd.Code))
.DataBinding(binding => {
binding.Ajax().Select(this.Model.AjaxSelectMethod);
binding.Ajax().Update(this.Model.AjaxUpdateMethod);
})
.Columns(columns => {
columns.Bound(icd => icd.ICDType.Name).Title("ICD 9/10");
columns.Bound(icd => icd.Code);
columns.Bound(icd => icd.Description);
columns.Bound(icd => icd.HCC.Description).Title("HCC Category")
columns.Command(commands => commands.Delete()).Title("Actions").Width(90);
})
.Editable(editing => editing.Mode(GridEditMode.InCell).DefaultDataItem(new ICD()))
.ToolBar(commands => {
commands.Insert();
commands.SubmitChanges();
})
.Sortable()
.Filterable()
.Pageable(paging => paging.PageSize(12))
.Render();
The problem is that both ICD and HCC have properties named "Description", and I have no control over that. Is there a way to tell Telerik to call them different things in the JavaScript it generates? Something like ICDDescription and HCCDescription?
Currently you cannot alias the properties. What you can do is create a ViewModel object with where the properties are named uniquely. Then bind the grid to the ViewModel object. Here is a code snippet:
public class ICDViewModel
{
public string Description
{
get;
set;
}
public string HCCDescription
{
get;
set;
}
// The rest of the properties of the original ICD class
}
Then you need to change the type of Model.ICDs to use ICDViewModel. You can use the Select extension method to map ICD to ICDViewModel:
Model.ICDs = icds.Select(icd => new ICDViewModel
{
Description = icd.Description,
HCCDescription = icd.HCC.Description
/* set the rest of the ICD properties */
});