Ids inference

Implicit conversion

Several places in the Elasticsearch API expect an instance of the Id type to be passed. This is a special type that you can implicitly convert to from the following types

Int32
Int64
String
Guid

Methods that take an Id can be passed any of these types and they will be implicitly converted to an instance of Id

Id idFromInt = 1;
Id idFromLong = 2L;
Id idFromString = "hello-world";
Id idFromGuid = new Guid("D70BD3CF-4E38-46F3-91CA-FCBEF29B148E");

Expect(1).WhenSerializing(idFromInt);
Expect(2).WhenSerializing(idFromLong);
Expect("hello-world").WhenSerializing(idFromString);
Expect("d70bd3cf-4e38-46f3-91ca-fcbef29b148e").WhenSerializing(idFromGuid);

Inferring Id from a type

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Sometimes a method takes an object instance and the client requires an Id from that instance to build up a path. There is no implicit conversion from any object to Id, but we can call Id.From.

Imagine your codebase has the following type that we want to index into Elasticsearch

class MyDTO
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public string OtherName { get; set; }
}

By default NEST will try to find a property called Id on the class using reflection and create a cached delegate based on the property getter

var dto = new MyDTO
{
    Id = new Guid("D70BD3CF-4E38-46F3-91CA-FCBEF29B148E"),
    Name = "x",
    OtherName = "y"
};

Expect("d70bd3cf-4e38-46f3-91ca-fcbef29b148e").WhenInferringIdOn(dto);

Using connection settings, you can specify a different property that NEST should use to infer Id for the document. Here we instruct NEST to infer the Id for MyDTO based on its Name property

WithConnectionSettings(x => x
    .DefaultMappingFor<MyDTO>(m => m
        .IdProperty(p => p.Name)
    )
).Expect("x").WhenInferringIdOn(dto);

Inference rules are cached per ConnectionSettings instance.

Because the cache is per ConnectionSettings instance, we can create another ConnectionSettings instance with different inference rules

WithConnectionSettings(x => x
    .DefaultMappingFor<MyDTO>(m => m
        .IdProperty(p => p.OtherName)
    )
).Expect("y").WhenInferringIdOn(dto);

DefaultMappingFor also has a non generic overload for the more dynamic use-cases.

WithConnectionSettings(x => x
    .DefaultMappingFor(typeof(MyDTO), m => m
        .IdProperty(typeof(MyDTO).GetProperty(nameof(MyDTO.Name)).Name)
    )
).Expect("x").WhenInferringIdOn(dto);

Using the ElasticsearchType attribute

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Another way to control Id inference is to mark the type with an ElasticsearchType attribute, setting IdProperty to the name of the property that should be used for the document id

[ElasticsearchType(IdProperty = nameof(Name))]
class MyOtherDTO
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public string OtherName { get; set; }
}

Now when we infer the id we expect it to be the value of the Name property without doing any configuration on the ConnectionSettings

var dto = new MyOtherDTO
{
    Id = new Guid("D70BD3CF-4E38-46F3-91CA-FCBEF29B148E"),
    Name = "x",
    OtherName = "y"
};

Expect("x").WhenInferringIdOn(dto);

Using Mapping inference on ConnectionSettings

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This attribute is cached statically/globally, however an inference rule on ConnectionSettings for the type will still win over the attribute.

Here we demonstrate this by creating a different ConnectionSettings instance that will infer the document id from the property OtherName:

WithConnectionSettings(x => x
    .DefaultMappingFor<MyOtherDTO>(m => m
        .IdProperty(p => p.OtherName)
    )
).Expect("y").WhenInferringIdOn(dto);

Disabling Id inference

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You can configure the client to disable Id inference on a CLR type basis

WithConnectionSettings(x => x
    .DefaultMappingFor<MyOtherDTO>(m => m
        .DisableIdInference()
    )
).Expect(null).WhenInferringIdOn(dto);

or globally for all types

WithConnectionSettings(x => x.DefaultDisableIdInference())
    .Expect(null).WhenInferringIdOn(dto);

Once disabled globally, Id inference cannot be enabled per type

WithConnectionSettings(x => x
    .DefaultDisableIdInference()
    .DefaultMappingFor<MyOtherDTO>(m => m
        .DisableIdInference(disable: false)
    )
).Expect(null).WhenInferringIdOn(dto);

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