test: add project examples

example/spring-data-mongodb/src/main/kotlin/com/github/inflab/example/spring/data/mongodb/repository/ProjectRepository.kt

@@ -0,0 +1,44 @@
+package com.github.inflab.example.spring.data.mongodb.repository
+
+import com.github.inflab.spring.data.mongodb.core.aggregation.aggregation
+import org.springframework.data.mongodb.core.MongoTemplate
+import org.springframework.data.mongodb.core.aggregation.Aggregation.REMOVE
+import org.springframework.data.mongodb.core.aggregation.AggregationResults
+import org.springframework.data.mongodb.core.aggregation.ComparisonOperators
+import org.springframework.data.mongodb.core.aggregation.ConditionalOperators
+import org.springframework.stereotype.Repository
+
+@Repository
+class ProjectRepository(
+    private val mongoTemplate: MongoTemplate,
+) {
+
+    data class Author(val first: String, val last: String, val middle: String?)
+    data class TitleAndAuthorDto(
+        val id: String,
+        val title: String,
+        val author: Author,
+    )
+
+    /**
+     * @see <a href="https://www.mongodb.com/docs/manual/reference/operator/aggregation/project/#conditionally-exclude-fields">Conditionally Exclude Fields</a>
+     */
+    fun excludeConditionally(): AggregationResults<TitleAndAuthorDto> {
+        val aggregation = aggregation {
+            project {
+                +"title"
+                "author.first" alias "author.first"
+                "author.last" alias "author.last"
+                "author.middle" expression ConditionalOperators.`when`(
+                    ComparisonOperators.valueOf("author.middle").equalToValue(""),
+                ).thenValueOf(REMOVE).otherwiseValueOf("author.middle")
+            }
+        }
+
+        return mongoTemplate.aggregate(aggregation, BOOKS, TitleAndAuthorDto::class.java)
+    }
+
+    companion object {
+        const val BOOKS = "books"
+    }
+}

example/spring-data-mongodb/src/main/kotlin/com/github/inflab/example/spring/data/mongodb/repository/SortByCountRepository.kt

@@ -10,18 +10,18 @@ class SortByCountRepository(
     private val mongoTemplate: MongoTemplate,
 ) {
 
-    data class IdAndCount(val id: String, val count: Int)
+    data class IdAndCountDto(val id: String, val count: Int)
 
     /**
      * @see <a href="https://www.mongodb.com/docs/manual/reference/operator/aggregation/sortByCount/#example">Example</a>
      */
-    fun sortByTags(): AggregationResults<IdAndCount> {
+    fun sortByTags(): AggregationResults<IdAndCountDto> {
         val aggregation = aggregation {
             unwind { path("tags") }
             sortByCount("tags")
         }
 
-        return mongoTemplate.aggregate(aggregation, EXHIBITS, IdAndCount::class.java)
+        return mongoTemplate.aggregate(aggregation, EXHIBITS, IdAndCountDto::class.java)
     }
 
     companion object {

example/spring-data-mongodb/src/test/kotlin/com/github/inflab/example/spring/data/mongodb/repository/ProjectRepositoryTest.kt

@@ -0,0 +1,38 @@
+package com.github.inflab.example.spring.data.mongodb.repository
+
+import com.github.inflab.example.spring.data.mongodb.extension.makeMongoTemplate
+import io.kotest.core.spec.style.FreeSpec
+import io.kotest.matchers.shouldBe
+import org.bson.Document
+
+internal class ProjectRepositoryTest : FreeSpec({
+    val mongoTemplate = makeMongoTemplate()
+    val sortByCountRepository = ProjectRepository(mongoTemplate)
+
+    beforeSpec {
+        val documents = listOf(
+            mapOf("_id" to 1, "title" to "abc123", "isbn" to "0001122223334", "author" to mapOf("last" to "zzz", "first" to "aaa"), "copies" to 5, "lastModified" to "2016-07-28"),
+            mapOf("_id" to 2, "title" to "Baked Goods", "isbn" to "9999999999999", "author" to mapOf("last" to "xyz", "first" to "abc", "middle" to ""), "copies" to 2, "lastModified" to "2017-07-21"),
+            mapOf("_id" to 3, "title" to "Ice Cream Cakes", "isbn" to "8888888888888", "author" to mapOf("last" to "xyz", "first" to "abc", "middle" to "mmm"), "copies" to 5, "lastModified" to "2017-07-22"),
+        ).map(::Document)
+
+        mongoTemplate.insert(documents, ProjectRepository.BOOKS)
+    }
+
+    "excludeConditionally" {
+        // when
+        val result = sortByCountRepository.excludeConditionally()
+
+        // then
+        result.mappedResults.map { it.title } shouldBe listOf(
+            "abc123",
+            "Baked Goods",
+            "Ice Cream Cakes",
+        )
+        result.mappedResults.map { it.author.middle } shouldBe listOf(
+            null,
+            null,
+            "mmm",
+        )
+    }
+})