Pom.xml: 
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>ru.edu.penzgtu</groupId>
    <artifactId>lab</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.6.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.xerial</groupId>
            <artifactId>sqlite-jdbc</artifactId>
            <version>3.30.1</version>
        </dependency>
        <dependency>
            <groupId>com.github.gwenn</groupId>
            <artifactId>sqlite-dialect</artifactId>
            <version>0.1.1</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <scope>annotationProcessor</scope>
        </dependency>
        <dependency>
            <groupId>io.swagger.core.v3</groupId>
            <artifactId>swagger-annotations</artifactId>
            <version>2.2.8</version>
        </dependency>
        <dependency>
            <groupId>org.springdoc</groupId>
            <artifactId>springdoc-openapi-ui</artifactId>
            <version>1.6.14</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>  </dependencies>

</project>

application.properties: 
server.port=8086

spring.datasource.driver-class-name=org.sqlite.JDBC
spring.datasource.url=jdbc:sqlite:lab_db.db
spring.datasource.username=user
spring.datasource.password=pass

spring.jpa.database-platform=org.sqlite.hibernate.dialect.SQLiteDialect
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

App.java
package ru.edu.penzgtu;

import io.swagger.v3.oas.annotations.OpenAPIDefinition;
import io.swagger.v3.oas.annotations.info.Contact;
import io.swagger.v3.oas.annotations.info.Info;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;

@OpenAPIDefinition(
        info = @Info(
                title = "PenzGTU Java Lab API",
                description = "Api fro labs", version = "1.0.0",
                contact = @Contact(
                        name = "Student PenzGTU",
                        email = "my_mail@mail.dev"
                )
        )
)

@SpringBootApplication
@EnableWebMvc
public class App {
    public static void main (String[] args) {
        SpringApplication.run(App.class, args);
    }
}

// Vendor.java
package ru.edu.penzgtu.entity;

import javax.persistence.*;
import javax.validation.constraints.NotNull;
import java.util.List;
import java.util.Objects;

@Entity
@Table(name = "vendors")
public class Vendor {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @NotNull
    @Column(name = "name")
    private String name;

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(
        name = "vendors_graphic_cards",
        joinColumns = @JoinColumn(name = "vendor_id", referencedColumnName = "id"),
        inverseJoinColumns = @JoinColumn(name = "graphic_card_id", referencedColumnName = "id")
    )
    private List<GraphicCard> graphicCards;

    public Vendor() {
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<GraphicCard> getGraphicCards() {
        return graphicCards;
    }

    public void setGraphicCards(List<GraphicCard> graphicCards) {
        this.graphicCards = graphicCards;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Vendor vendor = (Vendor) o;
        return Objects.equals(id, vendor.id) &&
                Objects.equals(name, vendor.name) &&
                Objects.equals(graphicCards, vendor.graphicCards);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name, graphicCards);
    }
}

GraphicCard.java
package ru.edu.penzgtu.entity;

import javax.persistence.*;
import java.util.List;
import java.util.Objects;

@Entity
@Table(name = "graphic_cards")
public class GraphicCard {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @Column(name = "name")
    private String name;

    @ManyToMany(mappedBy = "graphicCards")
    private List<Vendor> vendors;

    public GraphicCard() {
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Vendor> getVendors() {
        return vendors;
    }

    public void setVendors(List<Vendor> vendors) {
        this.vendors = vendors;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        GraphicCard graphicCard = (GraphicCard) o;
        return Objects.equals(id, graphicCard.id) &&
                Objects.equals(name, graphicCard.name) &&
                Objects.equals(vendors, graphicCard.vendors);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name, vendors);
    }
}

GraphicCardRepository.java
package ru.edu.penzgtu.repo;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import ru.edu.penzgtu.entity.GraphicCard;

@Repository
public interface GraphicCardRepository extends JpaRepository<GraphicCard, Long> {
}

VendorRepository.java
package ru.edu.penzgtu.repo;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import ru.edu.penzgtu.entity.Vendor;

@Repository
public interface VendorRepository extends JpaRepository<Vendor, Long> {
}

VendorService.java

package ru.edu.penzgtu.service;

import org.springframework.stereotype.Service;
import ru.edu.penzgtu.dto.VendorDto;
import ru.edu.penzgtu.entity.Vendor;
import ru.edu.penzgtu.repo.VendorRepository;
import ru.edu.penzgtu.service.mapper.VendorMapper;

import java.util.List;

@Service
public class VendorService {
    private final VendorRepository vendorRepository;
    private final VendorMapper vendorMapper;

    public VendorService(VendorRepository vendorRepository, VendorMapper vendorMapper) {
        this.vendorRepository = vendorRepository;
        this.vendorMapper = vendorMapper;
    }

    public List<VendorDto> findAllVendors() {
        return vendorMapper.toListDto(vendorRepository.findAll());
    }

    public VendorDto findVendorById(Long id) {
        Vendor vendor = vendorRepository.findById(id)
                .orElseThrow(() -> new RuntimeException(“Vendor not found”));
        return vendorMapper.toDto(vendor);
    }
    
    public void saveVendor(VendorDto vendorDto) {
        Vendor vendor = vendorMapper.toEntity(vendorDto);
        vendorRepository.save(vendor);
    }
    
    public void updateVendor(VendorDto newVendor) {
        Vendor oldVendor = vendorRepository.findById(newVendor.getId())
                .orElseThrow(() -> new RuntimeException(“Vendor not found”));

        oldVendor.setName(newVendor.getName());
    
        vendorRepository.save(oldVendor);
    }

    public void deleteVendorById(Long id) {
        vendorRepository.deleteById(id);
    }
}

GraphicCardService.java

package ru.edu.penzgtu.service;

import org.springframework.stereotype.Service;
import ru.edu.penzgtu.dto.GraphicCardDto;
import ru.edu.penzgtu.entity.GraphicCard;
import ru.edu.penzgtu.repo.GraphicCardRepository;
import ru.edu.penzgtu.service.mapper.GraphicCardMapper;

import java.util.List;

@Service
public class GraphicCardService {
    private final GraphicCardRepository graphicCardRepository;
    private final GraphicCardMapper graphicCardMapper;

    public GraphicCardService(GraphicCardRepository graphicCardRepository, GraphicCardMapper graphicCardMapper) {
        this.graphicCardRepository = graphicCardRepository;
        this.graphicCardMapper = graphicCardMapper;
    }

    public List<GraphicCardDto> findAllGraphicCards() {
        return graphicCardMapper.toListDto(graphicCardRepository.findAll());
    }

    public GraphicCardDto findGraphicCardById(Long id) {
        GraphicCard graphicCard = graphicCardRepository.findById(id)
                .orElseThrow(() -> new RuntimeException(“GraphicCard not found”));
        return graphicCardMapper.toDto(graphicCard);
    }

    public void saveGraphicCard(GraphicCardDto graphicCardDto) {
        GraphicCard graphicCard = graphicCardMapper.toEntity(graphicCardDto);
        graphicCardRepository.save(graphicCard);
    }

    public void updateGraphicCard(GraphicCardDto newGraphicCard) {
        GraphicCard oldGraphicCard = graphicCardRepository.findById(newGraphicCard.getId())
                .orElseThrow(() -> new RuntimeException(“GraphicCard not found”));

        oldGraphicCard.setName(newGraphicCard.getName());

        graphicCardRepository.save(oldGraphicCard);
    }

    public void deleteGraphicCardById(Long id) {
        graphicCardRepository.deleteById(id);
    }
}

VendorController.java

package ru.edu.penzgtu.controller;

import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.tags.Tag;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.;
import ru.edu.penzgtu.dto.VendorDto;
import ru.edu.penzgtu.service.VendorService;

import javax.validation.Valid;
import javax.validation.constraints.Min;
import java.util.List;

@RestController
@RequestMapping(“/vendors”)
@Tag(name = “Vendors”, description = “Operations related to vendors”)
public class VendorController {
    private final VendorService vendorService;

    public VendorController(VendorService vendorService) {
        this.vendorService = vendorService;
    }

    @Operation(
        summary = “Get all vendors”, description = “Fetch all vendors from the database”
    )
    @GetMapping
    public List<VendorDto> findAll() {
        return vendorService.findAllVendors();
    }

    @Operation(
        summary = “Get a vendor by ID”, description = “Fetch a single vendor by ID from the database”
    )
    @GetMapping(“/vendor/{id}”)
    public VendorDto getById(@PathVariable @Min(0) long id) {
        return vendorService.findVendorById(id);
    }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public void createVendor(@RequestBody @Valid VendorDto vendor) {
        vendorService.saveVendor(vendor);
    }

    @Operation(
        summary = “Update vendor details”, description = “Update the details of a vendor in the database”
    )
    @PutMapping(“/vendor”)
    public void updateVendor(@RequestBody @Valid VendorDto vendor) {
        vendorService.updateVendor(vendor);
    }

    @Operation(
        summary = “Delete a vendor by ID”, description = “Delete a vendor by ID from the database”
    )
    @DeleteMapping(“/vendor/{id}”)
    @ResponseStatus(HttpStatus.NO_CONTENT)
    public void deleteVendor(@PathVariable @Min(0) long id) {
        vendorService.deleteVendorById(id);
    }
}

GraphicCardController.java

package ru.edu.penzgtu.controller;

import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.tags.Tag;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.;
import ru.edu.penzgtu.dto.GraphicCardDto;
import ru.edu.penzgtu.service.GraphicCardService;

import javax.validation.Valid;
import javax.validation.constraints.Min;
import java.util.List;

@RestController
@RequestMapping(“/graphic-cards”)
@Tag(name = “Graphic Cards”, description = “Operations related to graphic cards”)
public class GraphicCardController {
    private final GraphicCardService graphicCardService;

    public GraphicCardController(GraphicCardService graphicCardService) {
        this.graphicCardService = graphicCardService;
    }

    @Operation(
        summary = “Get all graphic cards”, description = “Fetch all graphic cards from the database”
    )
    @GetMapping
    public List<GraphicCardDto> findAll() {
        return graphicCardService.findAllGraphicCards();
    }

    @Operation(
        summary = “Get a graphic card by ID”, description = “Fetch a single graphic card by ID from the database”
    )
    @GetMapping(“/graphic-card/{id}”)
    public GraphicCardDto getById(@PathVariable @Min(0) long id) {
        return graphicCardService.findGraphicCardById(id);
    }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public void createGraphicCard(@RequestBody @Valid GraphicCardDto graphicCard) {
        graphicCardService.saveGraphicCard(graphicCard);
    }

    @Operation(
        summary = “Update graphic card details”, description = “Update the details of a graphic card in the database”
    )
    @PutMapping(“/graphic-card”)
    public void updateGraphicCard(@RequestBody @Valid GraphicCardDto graphicCard) {
        graphicCardService.updateGraphicCard(graphicCard);
    }

    @Operation(
        summary = “Delete a graphic card by ID”, description = “Delete a graphic card by ID from the database”
    )
    @DeleteMapping(“/graphic-card/{id}”)
    @ResponseStatus(HttpStatus.NO_CONTENT)
    public void deleteGraphicCard(@PathVariable @Min(0) long id) {
        graphicCardService.deleteGraphicCardById(id);
    }
}

VendorMapper.java

package ru.edu.penzgtu.service.mapper;

import org.springframework.stereotype.Service;
import ru.edu.penzgtu.dto.VendorDto;
import ru.edu.penzgtu.entity.Vendor;

import java.util.List;
import java.util.stream.Collectors;

@Service
public class VendorMapper {
    public List<VendorDto> toListDto(List<Vendor> vendors) {
        return vendors.stream().map(this::toDto).collect(Collectors.toList());
    }

    public VendorDto toDto(Vendor vendor) {
        VendorDto dto = new VendorDto();
        dto.setId(vendor.getId());
        dto.setName(vendor.getName());
        return dto;
    }

    public Vendor toEntity(VendorDto vendorDto) {
        Vendor vendor = new Vendor();
        vendor.setId(vendorDto.getId());
        vendor.setName(vendorDto.getName());
        return vendor;
    }
}

GraphicCardMapper.java

package ru.edu.penzgtu.service.mapper;

import org.springframework.stereotype.Service;
import ru.edu.penzgtu.dto.GraphicCardDto;
import ru.edu.penzgtu.entity.GraphicCard;
import ru.edu.penzgtu.entity.Vendor;

import java.util.List;
import java.util.stream.Collectors;

@Service
public class GraphicCardMapper {

    public List<GraphicCardDto> toListDto(List<GraphicCard> graphicCards) {
        return graphicCards.stream().map(this::toDto).collect(Collectors.toList());
    }

    public GraphicCardDto toDto(GraphicCard graphicCard) {
        GraphicCardDto dto = new GraphicCardDto();
        dto.setId(graphicCard.getId());
        dto.setName(graphicCard.getName());
        dto.setVendors(graphicCard.getVendors().stream().map(Vendor::getName)
                .collect(Collectors.toList()));
        return dto;
    }

    public GraphicCard toEntity(GraphicCardDto graphicCardDto) {
        GraphicCard graphicCard = new GraphicCard();
        graphicCard.setId(graphicCardDto.getId());
        graphicCard.setName(graphicCardDto.getName());
        return graphicCard;
    }
}

вот код, просто запомни его для дальнейшей работы с ним