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Graph/dto-mapping-nested-models

Pattern

DTO Mapping for Nested Models

dto-mapping-nested-models

A recurring model/DTO mismatch where nested ORM objects are serialized as full objects, but the API contract expects derived primitives, leading to manual mapping via DTO separation or explicit validator transformations.

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Updated5/1/2026

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30 linked nodes

Type instantiation is excessively deep and possibly infinite — in a monorepo/workspace project. Tension: on seemingly benign types like this. Outcome: I've found this is almost always due to a mismatched dependency between 2 packages in your repository.

I have an endpoint that takes a Pydantic model, `Foo`, as a query parameter. Outcome: parsing fails even without nesting.

Normally, the response looks like this: — I have a model, called Candidate that I'm trying to return, two of the fields refer to another model, StaffMember. Tension: However, I don't want any nested fields.

that will give me 3 levels deep of nodes in my json output — I have a many to many self referential relationship. Tension: is there a way to do that so it goes as many levels deep as needed until nodes = [] ? Outcome: Do I need to use something like marshmallow-sqlalchemy ?

When I use `author_id: int | None`, I get an error saying that a required field is missing. — requesting an endpoint that accepts the above model as its JSON body. Tension: The annotations don't actually do anything by themselves. Outcome: the model works as expected without errors.

PermissionSchema.model_validate(permission) cannot build a schema from an SQLModel instance

FastAPI cannot choose the correct model for a Union request body when one variant has an enum field

The `exclude_none` parameter to `model.model_dump` would apply to all entries of response, so it is not suitable. — Response is serialized/dumped as a JSON. Tension: I want attr2 to be included only if it is non-null. Importantly, `stuff1` should be included regardless of its type (null or int). Outcome: Pydantic v2 has custom serialization which allows one to control how objects are converted to JSON, but I am using 1.10.

FastAPI does not know about Lizard, Dog and Cat schemas in OpenAPI

SQLModel/Pydantic serializes the `categories: list[Category]` field as nested objects, but the API response needs `categories` as `list[str]` containing `Category.name` values.

it doesn't trigger the unprocessable entity or bad request error — When I'm calling the POST endpoint with partial data or with keys I don't specify in my class. Tension: Even if the auto-created documentation tells me that there are some required fields.

I have had this brain teaser for a day now — map certain models to build an API (Learning Management System API) using FastAPI. Outcome: I pretty much just used BaseRole as a Mixin where I need it to be.

There is no example on how to use enum mapping with postgres and hibernate 6. — I am migrating from hibernate 5 to 6. Tension: As @TypeDef is no more available I don't know how I can map my enum type to my database column.

This only give me the Event type without the nested `Owner` property/relation. — I have a model with a relation to a separate model. I’m now querying the object and the related object. Tension: But how do I get a typescript type so that I can pass this object to subcomponents of my react component? Outcome: This only give me the Event type without the nested `Owner` property/relation.

it seems that is not working for me — Spring Data Couchbase and I have an entity that maps some of the fields of a document. Tension: I need all the other fields to be mapped to a Map<String, Object>.

After migrating from field injection to constructor-based injection, Spring throws a BeanCreationException when instantiating `exampleCommand` because it cannot resolve a constructor parameter for the DTO passed via `beanFactory.getBean(Command.class, inputDto)`.

Mono.just(authentication.getPrincipal()) .ofType(UserDto.class) .filter(this::matchesExistingUser) // needs DTO .map(UserAuthenticationToken::from); // needs User, but. Outcome: So, there you would call your `userService.find(userDto)` and use this `Tuple2` downstream for those respective `filter` and `map` operators.

org.hibernate.query.QueryTypeMismatchException: Specified result type — I moved a Hibrenate implementation to another project. From com.mvc.data to com.mvc.frontend. Tension: Notice that it's the same type. Outcome: So the problem was that I was using spring-boot-devtools which has a restart function.

a fundamental property of value objects is that they should not be null — your `BankUpdateRequest`. Tension: which conflicts with the optional fields in your `BankUpdateRequest`. Outcome: allow `null` in DTOs.

I would like to use an existent Parent instance to create a child instance — with lombok Annotations. Tension: with all parent fields filled, and be able to complement with child properties. Outcome: instead of a parent's "field by field" solution.

there is some requirement where in particular 2-3 APIs, I dont want this prefix to come — We have used MappingJackson2HttpMessageConverter -> JsonPrefix to attach some prefix. Tension: This works corrects and provides response as expected. Outcome: So is there any way to achieve the same?

the `"type"` property is missing from the array elements in the obfuscated form — after running through ProGuard. Tension: This causes Jackson to deserialize those objects incorrectly. Outcome: allows the example to run successfully even after obfuscation.

I want to use this CRUD service when my class is serialized — I have a CRUD service in Spring Boot, and I'm using a custom serializer with a class that extends `JsonSerializer`. Tension: I've tried several approaches without success.

A container entity needs to persist a List of objects whose types are subclasses of a common base class. Because the base is annotated with @MappedSuperclass, attempts to map the list using generics/relationship annotations fail.

IntelliJ doesn't generate a mapper when I save files. Tension: In Eclipse, when I modify a Mapstruct mapper Interface and save it, the IDE generates the related implementation immediately. Outcome: I must perform a mvn `mvn generate-sources` or a `clean install` to do the same.

Using a single @SequenceGenerator definition in a mapped superclass causes Product and Order entities to share the same database sequence, so ids are generated from the same sequence. The goal is to have separate sequence names per entity without relying on Hibernate-specific generator classes.

{ "a": "this-is-ignored", "b": "uses-this-value" }. Tension: It works perfect when either `a` or `b` are present, and when both are present and `b` comes after `a`. Outcome: custom deserializer for whole class.

This works when I fetch into a record, but not my own pojo — I have tried many different variations including passing Long[].class to DSL.field. Tension: I just get the following. Outcome: please make sure it accommodates fetching multiple arrays of ids related to TEACHER with corresponding where/and clauses.

Hibernate ORM doesn’t bother checking if a collection element is deeply equal to an element of the initial state — @ElementCollection(fetch = FetchType.EAGER). Tension: the user passes the fields they want. Outcome: avoid replacing objects in that case.

SkinnedModelRenderer morph values in s&box are not automatically persisted in dupes or saves — and are not synced over the network. Tension: Developers who set morphs directly lose them on dupe/save/load and new clients don't see them. Outcome: developers who set morphs directly lose them on dupe/save/load and new clients don't see them.

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