Add DataLoader example. (#396)

examples/spring/src/main/kotlin/com/expediagroup/graphql/examples/dataloaders/DataLoaderConfiguration.kt

@@ -0,0 +1,27 @@
+package com.expediagroup.graphql.examples.dataloaders
+
+import com.expediagroup.graphql.examples.model.Company
+import com.expediagroup.graphql.examples.query.CompanyService
+import com.expediagroup.graphql.spring.execution.DataLoaderRegistryFactory
+import org.dataloader.DataLoader
+import org.dataloader.DataLoaderRegistry
+import org.springframework.context.annotation.Bean
+import org.springframework.context.annotation.Configuration
+import java.util.concurrent.CompletableFuture
+
+@Configuration
+class DataLoaderConfiguration(private val companyService: CompanyService) {
+    @Bean
+    fun dataLoaderRegistryFactory(): DataLoaderRegistryFactory {
+        return object : DataLoaderRegistryFactory {
+            override fun generate(): DataLoaderRegistry {
+                val registry = DataLoaderRegistry()
+                val companyLoader = DataLoader<Int, Company> { ids ->
+                    CompletableFuture.supplyAsync { companyService.getCompanies(ids) }
+                }
+                registry.register("companyLoader", companyLoader)
+                return registry
+            }
+        }
+    }
+}

examples/spring/src/main/kotlin/com/expediagroup/graphql/examples/model/Organization.kt

@@ -0,0 +1,13 @@
+package com.expediagroup.graphql.examples.model
+
+import com.expediagroup.graphql.annotations.GraphQLIgnore
+
+data class Employee(
+    val name: String,
+    @GraphQLIgnore
+    val companyId: Int
+) {
+    lateinit var company: Company
+}
+
+data class Company(val id: Int, val name: String)

examples/spring/src/main/kotlin/com/expediagroup/graphql/examples/query/OrganizationQuery.kt

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+package com.expediagroup.graphql.examples.query
+
+import com.expediagroup.graphql.annotations.GraphQLDescription
+import com.expediagroup.graphql.examples.model.Company
+import com.expediagroup.graphql.examples.model.Employee
+import com.expediagroup.graphql.spring.operations.Query
+import graphql.schema.DataFetcher
+import graphql.schema.DataFetchingEnvironment
+import org.springframework.beans.factory.BeanFactory
+import org.springframework.beans.factory.BeanFactoryAware
+import org.springframework.context.annotation.Scope
+import org.springframework.stereotype.Component
+import java.util.concurrent.CompletableFuture
+
+@Component
+class CompanyService {
+    private val companies = listOf(
+        Company(id = 1, name = "FirstCompany"),
+        Company(id = 2, name = "SecondCompany")
+    )
+
+    fun getCompanies(ids: List<Int>): List<Company> = companies
+}
+
+@Component
+class EmployeeQuery : Query {
+    private val employees = listOf(
+        Employee(name = "Mike", companyId = 1),
+        Employee(name = "John", companyId = 1),
+        Employee(name = "Steve", companyId = 2)
+    )
+
+    @GraphQLDescription("Get all employees")
+    fun employees(): List<Employee> {
+        return employees
+    }
+}
+
+@Component("CompanyDataFetcher")
+@Scope("prototype")
+class CompanyDataFetcher : DataFetcher<CompletableFuture<Company>>, BeanFactoryAware {
+    private lateinit var beanFactory: BeanFactory
+
+    override fun setBeanFactory(beanFactory: BeanFactory) {
+        this.beanFactory = beanFactory
+    }
+
+    override fun get(environment: DataFetchingEnvironment): CompletableFuture<Company> {
+        val companyId = environment.getSource<Employee>().companyId
+        return environment
+            .getDataLoader<Int, Company>("companyLoader")
+            .load(companyId)
+    }
+}