Duplicated Fields for Faster Querying

One option to speed up queries against the JSONB documents is by duplicating a property or field within the JSONB structure as a separate database column on the document table. When you issue a Linq query using this duplicated property or field, Marten is able to write the SQL query to run against the duplicated field instead of using JSONB operators. This of course only helps for queries using the duplicated field.

TIP

we strongly recommend using Computed Indexes/Calculated Indexes over duplicated fields for most cases to speed up queries. Calculated indexes optimize the querying of a document type without incurring potentially expensive schema changes and extra runtime insert costs.

Also note that there are few cases where calculated index does not work i.e DateTime, DateTimeOffset fields, resort to using duplicated fields for these.

To create a duplicated field, you can use the [DuplicateField] attribute like this:

[PropertySearching(PropertySearching.ContainmentOperator)]
public class Employee
{
    public int Id;

    // You can optionally override the Postgresql
    // type for the duplicated column in the document
    // storage table
    [DuplicateField(PgType = "text")]
    public string Category;

    // Defining a duplicate column with not null constraint
    [DuplicateField(PgType = "text", NotNull = true)]
    public string Department;
}

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Or by using the fluent interface off of StoreOptions:

var store = DocumentStore.For(options =>
{
    // Add a gin index to the User document type
    options.Schema.For<User>().GinIndexJsonData();

    // Adds a basic btree index to the duplicated
    // field for this property that also overrides
    // the Postgresql database type for the column
    options.Schema.For<User>().Duplicate(x => x.FirstName, pgType: "varchar(50)");

    // Defining a duplicate column with not null constraint
    options.Schema.For<User>().Duplicate(x => x.Department, pgType: "varchar(50)", notNull: true);

    // Customize the index on the duplicated field
    // for FirstName
    options.Schema.For<User>().Duplicate(x => x.FirstName, configure: idx =>
    {
        idx.Name = "idx_special";
        idx.Method = IndexMethod.hash;
    });

    // Customize the index on the duplicated field
    // for UserName to be unique
    options.Schema.For<User>().Duplicate(x => x.UserName, configure: idx =>
    {
        idx.IsUnique = true;
    });

    // Customize the index on the duplicated field
    // for LastName to be in descending order
    options.Schema.For<User>().Duplicate(x => x.LastName, configure: idx =>
    {
        idx.SortOrder = SortOrder.Desc;
    });
});

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In the case above, Marten would add an extra columns to the generated mt_doc_user table with first_name and department. Some users find duplicated fields to be useful for user supplied SQL queries.

Defining Not Null constraint

By default, the duplicate column is created with NULL constraint. If you want to define the duplicate column with a NOT NULL constraint, use NotNull property via DuplicateFieldAttribute or pass notNull: true for the Duplicate fluent interface. See the examples above.

Indexing

By default, Marten adds a btree index (the Postgresql default) to a searchable index, but you can also customize the generated index with the syntax shown above: The second nested closure argument is an optional mechanism to customize the database index generated for the duplicated field.