Entity Framework Core add unique constraint code-first

Question

I can t find way to add a unique constraint to my field with using attribute   public class User        Required      public int Id   get  set          Required          Index  IX FirstAndSecond   2  IsUnique   true   not supported by core     public string Email   get  set          Required      public string Password   get  set        I m using these packages     Microsoft EntityFrameworkCore    1 0 1     Microsoft EntityFrameworkCore SqlServer    1 0 1     Microsoft EntityFrameworkCore SqlServer Design    1 0 1     Microsoft EntityFrameworkCore Tools    1 0 0-preview2-final

User · Answer

We can add Unique key index by using fluent api  Below code worked for me  protected override void OnModelCreating DbModelBuilder modelBuilder                 modelBuilder Entity lt User gt    Property p   gt  p Email  HasColumnAnnotation  Index   new IndexAnnotation new IndexAttribute  IX EmailIndex     IsUnique   true

User · Answer

Solution for EF Core  public class User       public int Id   get  set        public string Name   get  set        public string Passport   get  set       public class ApplicationContext   DbContext       public DbSet lt User gt  Users   get  set        public ApplicationContext                 Database EnsureCreated              protected override void OnConfiguring DbContextOptionsBuilder optionsBuilder                optionsBuilder UseSqlServer   Server  localdb  mssqllocaldb Database efbasicsappdb Trusted Connection True                protected override void OnModelCreating ModelBuilder modelBuilder                modelBuilder Entity lt User gt    HasAlternateKey u   gt  u Passport             or  modelBuilder Entity lt User gt    HasAlternateKey u   gt  new   u Passport  u Name             DB table will look like this   CREATE TABLE  dbo   Users         Id        INT            IDENTITY  1  1  NOT NULL       Name      NVARCHAR  MAX  NULL       Passport  NVARCHAR  450  NOT NULL      CONSTRAINT  PK Users  PRIMARY KEY CLUSTERED   Id  ASC       CONSTRAINT  AK Users Passport  UNIQUE NONCLUSTERED   Passport  ASC       Ref to EF Core docs

User · Answer

Ef core support unique configuration  protected override void OnModelCreating ModelBuilder builder      builder Entity lt Account gt         HasIndex account   gt  account Email         IsUnique       Ef core support multiple unique keys protected override void OnModelCreating ModelBuilder modelBuilder      modelBuilder Entity lt Account gt           HasKey account   gt  new   account Id  account Email  account RoleId        Don t forget run ef core command to make migration and update the database  gt  gt  dotnet ef migrations add MigrationName -c YourDbContextName  gt  gt  dotnet ef database update -c YourDbContextName

User · Answer

On EF core you cannot create Indexes using data annotations But you can do it using the Fluent API    Like this inside your  Db Context cs   protected override void OnModelCreating ModelBuilder builder        builder Entity lt User gt             HasIndex u   gt  u Email           IsUnique           or if you re using the overload with the buildAction   protected override void OnModelCreating ModelBuilder builder        builder Entity lt User gt  entity   gt            entity HasIndex e   gt  e Email  IsUnique                You can read more about it here   Indexes

User · Answer

To use it in EF core via model configuration  public class ApplicationCompanyConfiguration   IEntityTypeConfiguration lt Company gt        public void Configure EntityTypeBuilder lt Company gt  builder                builder ToTable  Company             builder HasIndex p   gt  p Name  IsUnique

User · Answer

Also if you want to create Unique constrains on multiple columns you can simply do this  following  Sampath s link   class MyContext   DbContext       public DbSet lt Person gt  People   get  set         protected override void OnModelCreating ModelBuilder modelBuilder                modelBuilder Entity lt Person gt                 HasIndex p   gt  new   p FirstName  p LastName                 IsUnique true            public class Person       public int PersonId   get  set        public string FirstName   get  set        public string LastName   get  set

User · Answer

The OP is asking about whether it is possible to add an Attribute to an Entity class for a Unique Key   The short answer is that it IS possible  but not an out-of-the-box feature from the EF Core Team  If you d like to use an Attribute to add Unique Keys to your Entity Framework Core entity classes  you can do what I ve posted here public class Company        Required       DatabaseGenerated DatabaseGeneratedOption Identity       public Guid CompanyId   get  set          Required       UniqueKey groupId   quot 1 quot   order  0        StringLength 100  MinimumLength   1       public string CompanyName   get  set          Required       UniqueKey groupId   quot 1 quot   order  1        StringLength 100  MinimumLength   1       public string CompanyLocation   get  set

User · Answer

For someone who is trying all these solution but not working try this one  it worked for me  protected override void OnModelCreating ModelBuilder builder         builder Entity lt User gt    Property t   gt  t Email  HasColumnAnnotation  Index   new IndexAnnotation new IndexAttribute  IX EmailIndex     IsUnique   true

User · Answer

None of these methods worked for me in  NET Core 2 2 but I was able to adapt some code I had for defining a different primary key to work for this purpose   In the instance below I want to ensure the OutletRef field is unique   public class ApplicationDbContext   IdentityDbContext               protected override void OnModelCreating ModelBuilder modelBuilder                        base OnModelCreating modelBuilder               modelBuilder Entity lt Outlet gt                     HasIndex o   gt  new   o OutletRef                        This adds the required unique index in the database  What it doesn t do though is provide the ability to specify a custom error message

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