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The new EF Core JSON Columns

In this article, we will see how to use the new JSON columns in EF Core 7.0.

JSON Columns

Most relational databases support columns that contain JSON documents. The JSON in these columns can be drilled into with queries. This allows, for example, filtering and sorting by the elements of the documents, as well as projection of elements out of the documents into results. JSON columns allow relational databases to take on some of the characteristics of document databases, creating a useful hybrid between the two.

EF7 contains provider-agnostic support for JSON columns, with an implementation for SQL Server. This support allows mapping of aggregates built from .NET types to JSON documents. Normal LINQ queries can be used on the aggregates, and these will be translated to the appropriate query constructs needed to drill into the JSON. EF7 also supports updating and saving changes to the JSON documents.

You can find more information about JSON columns in EF Core 7.0 in the documentation.

Mapping JSON Columns

In EF Core, aggregate types are defined using OwnsOne and OwnsMany. OwnsOne is used to map a single aggregate, and OwnsMany is used to map a collection of aggregates.

ToJson is used to map a property to a JSON column. The property can be of any type that can be serialized to JSON.

These aggregates can be mapped to JSON columns using the ToJson method. The following example shows how to map a JSON column to an aggregate type:

public class ContactDetails
{
    public Address Address { get; set; }
    public string? Phone { get; set; }
}

public class Address
{
    public Address(string street, string city, string postcode, string country)
    {
        Street = street;
        City = city;
        Postcode = postcode;
        Country = country;
    }

    public string Street { get; set; }
    public string City { get; set; }
    public string Postcode { get; set; }
    public string Country { get; set; }
}

public class Person : AggregateRoot<int>
{
    public string Name { get; set; } = null!;
    public ContactDetails ContactDetails { get; set; } = null!;
}

Above, we have defined an aggregate type ContactDetails that contains an Address and a Phone number. The aggregate type is configured in OnModelCreating using OwnsOne and ToJson. The Address property is mapped to a JSON column using ToJson, and the Phone property is mapped to a regular column. This requires just one call to ToJson() when configuring the aggregate type:


public class MyDbContext : AbpDbContext<MyDbContext>
{
    public DbSet<Person> Persons { get; set; }

    public MyDbContext(DbContextOptions<MyDbContext> options)
        : base(options)
    {
    }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        builder.Entity<Person>(b =>
        {
            b.ToTable(MyProjectConsts.DbTablePrefix + "Persons", MyProjecConsts.DbSchema);
            b.ConfigureByConvention();
            b.OwnsOne(x=>x.ContactDetails, c =>
            {
                c.ToJson();
                c.OwnsOne(cd => cd.Address);
            });
        });
    }
}

Querying JSON Columns

Queries into JSON columns work just the same as querying into any other aggregate type in EF Core. That is, just use LINQ! Here are some examples:

var persons = await (await GetDbSetAsync()).ToListAsync();

var contacts = await (await GetDbSetAsync()).Select(person => new
{
    person,
    person.ContactDetails.Phone,
    Addresses = person.ContactDetails.Address
}).ToListAsync();


var addresses = await (await GetDbSetAsync()).Select(person => new
{
    person,
    Addresses = person.ContactDetails.Address
}).ToListAsync();

Updating JSON Columns

You can update JSON columns using the Update method. The following example shows how to update a JSON column:

var person = await (await GetDbSetAsync()).FirstAsync();

person.ContactDetails.Phone = "123456789";
person.ContactDetails.Address = new Address("Street", "City", "Postcode", "Country");
await UpdateAsync(person, true);

Database View

References

https://docs.microsoft.com/en-us/ef/core/what-is-new/ef-core-7.0/whatsnew#json-columns

https://docs.microsoft.com/en-us/ef/core/modeling/owned-entities

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