EF Core version: 5.0.4 Database provider: Npgsql Target framework: .NET 5.0 Operating system: Windows 10 Code Now, let's say there is a user entity which has a column - MembershipType. See EF Core value converters for more information. . Applies to. However, EF Core doesn't auto-discover these converters, so you need to manually map the properties when creating the model:. However we use a custom string value to represent the enum in our database, so I have written a custom EnumToDbStringEquivalentConvertor to do this conversion and the database string value is specified as an attribute on each of the enum values in my model. Entity Framework Core uses ValueConverter to convert an object such as a strongly-typed id to a primitive type that can be stored into a DB. It just sees a custom type with no known conversion to a database type, so it assumes that it's an entity. EF Core complains that it doesn't know how to map our strongly-typed IDs (OrderId) to a database type. The wiring happens in HasConversion method in OnModelCreating. Now, we are able to map custom .NET types to a type the database understands and vice versa. Feedback. Entity Framework Core (EF) 2.1 introduced a new feature called Value Conversion. Luckily Entity Framework Core 2.1 (currently in preview) has a solution. The code is as follows: Model As described in the EF Core documentation: This, also, is not too complex. This long-awaited feature is especially popular among software engineers following the domain driven design (DDD) patterns. This works in EF Core 2.1.2 which I am using so no guarantees for older or newer versions (as the API states that these classes may be changed) but hopefully only small changes if there are issues. In this post I describe a solution to using strongly-typed IDs in your EF Core entities by using value converters and a custom IValueConverterSelector. Apply the [JsonConverter] attribute to a class or a struct that represents a custom value type. Luckily, there's a mechanism we can use to control this as of EF Core 2.1: value converters. Apply the [JsonConverter] attribute to the properties that require the custom converter. Today I want to show an example of how great are value converters in EF Core. Value converters allow property values to be converted when reading from or writing to the database. Introduction The feature that makes all this happen is called Value Conversions. Updated 10/5/2016: This post has been updated to use improved Entity Framework Core techniques which don't rely on internal APIs. - Microsoft Docs They are not persisted on their own; they belong to an entity. Choose one of the following approaches: Add an instance of the converter class to the JsonSerializerOptions.Converters collection. Data Protection is a nice feature in .NET Core, that abstracts the converter itself from inventing some half-broken encryption and hence it's a good idea to use it. So, It's not possible to write filter query directly like this: var users = dbContext.Users.Where (e => e.EmploymentRoles.Contains (Roles.Worker)).ToList (); because EF Core can't translate Custom ValueConverter to SQL and execute this on the server-side. The EF core model should look as shown in below snapshot. They have no identity. EF Core comes with built-in logic for snapshotting and comparing most standard types used in databases, so users don't usually need to worry about this topic. By default, value converters do not handle nulls so that a value converter for a non-nullable property (such as a primary key) can be used for correlated nullable properties, such as any corresponding foreign key properties. The code is as follows: Model 8 comments mattjohnsonpint commented on Mar 5, 2018 Use of value conversions may impact the ability of EF Core to translate expressions to SQL. This product . In this article: There are several characteristics that value objects have: They are immutable. It means you can have a property of any types you want as long as you tell EF how to convert to and from your type to any type it already knows. By deriving from this class, we can add our strongly-typed ID . Full list of built-in converters can be found here in the documentation. The configuration will be inside the UserProfile class: public class UserProfile : Profile { public UserProfile() { CreateMap<User, UserViewModel> ().IncludeMembers(u => u.Address, u => u.AdditionalInfo); CreateMap<Address, UserViewModel> (MemberList.None); CreateMap<AdditionalInfo, UserViewModel> (MemberList.None); } } The equality is based on properties. However, when a property is mapped through a value converter, EF Core needs to perform comparison on arbitrary user types, which may be complex. There are no warnings still now in 3.1.x, but this code will catch an error at the 5.x .NET. This post was written by Alina Popa, a software engineer on the .NET team. Out of the box, EF Core doesn't know anything about our strongly-typed ids. The base ValueConverterSelector in the EF Core framework is used to register all built-in value conversions between primitive types. So the following will enable a DateTime property (representing just the date) in the POCO to be useable with the actual SQL data being a string. public static void SetValueConverter (this Microsoft.EntityFrameworkCore.Metadata.IMutableProperty property, Microsoft.EntityFrameworkCore.Storage.ValueConversion . Creating a custom ValueConverter for EF Core. Implementing Seeding, Custom Conventions and Interceptors in EF Core 1.0 Introduction Entity Framework Core (EF Core) is a lightweight and extensible version of the Entity Framework (EF . Then you need to tell EF Core to both use that converter for DateOnly properties and to store those properties as date columns in the database. This conversion can be from one value to another of the same type (for example, encrypting strings) or from a value of one type to a value of another type (for example, converting enum values to and from strings in the database.) Which means that if we don't do anything, it will attempt to map ProductId to a ProductId table with a . 8 comments . Basically a value converter informs the EF engine how to store and materialize value type that it does not know by default. Here's another way of identifying the private properties that should be mapped to the database: First add the column attribute to the private property: [System.ComponentModel.DataAnnotations.Schema.Column] private string isActive { get; set; } Then use the presence of that attribute to identify private properties in your OnModelCreating method: EF Core string to datetime/datetimeoffset value converter example with CAST SQL generation - program.cs. A warning will be logged for such cases. In your context class, the one that inherits from DbContext, override ConfigureConventions like so: DataContext.cs Submit and view feedback for. Value conversion for a specific strongly-typed id. Simply speaking whenever the value is read or written your function is called and can do whatever transformation it wants. This column is supposed to hold an enum value - any one of Premium or Free. However we use a custom string value to represent the enum in our database, so I have written a custom EnumToDbStringEquivalentConvertor to do this conversion and the database string value is specified as an attribute on each of the enum values in my model. The creation of a value object is done through the constructor, and once created, its property values can't be changed. As mentioned above, EF Core ships with a set of pre-defined ValueConverter<TModel,TProvider> classes, found in the Microsoft.EntityFrameworkCore.Storage.ValueConversion namespace. 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