BAEL-2582 Building DSLs in Kotlin
* added basic SQL DSL * basic SQL DSL tests
This commit is contained in:
Denis Zhdanov
parent
46bad01ab9
commit
29c13ca801
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package com.baeldung.kotlin.dsl
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abstract class Condition {
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fun and(initializer: Condition.() -> Unit) {
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addCondition(And().apply(initializer))
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}
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fun or(initializer: Condition.() -> Unit) {
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addCondition(Or().apply(initializer))
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}
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infix fun String.eq(value: Any?) {
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addCondition(Eq(this, value))
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}
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protected abstract fun addCondition(condition: Condition)
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}
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open class CompositeCondition(private val sqlOperator: String) : Condition() {
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private val conditions = mutableListOf<Condition>()
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override fun addCondition(condition: Condition) {
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conditions += condition
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}
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override fun toString(): String {
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return if (conditions.size == 1) {
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conditions.first().toString()
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} else {
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conditions.joinToString(prefix = "(", postfix = ")", separator = " $sqlOperator ") {
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"$it"
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}
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}
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}
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}
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class And : CompositeCondition("and")
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class Or : CompositeCondition("or")
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class Eq(private val column: String, private val value: Any?) : Condition() {
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init {
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if (value != null && value !is Number && value !is String) {
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throw IllegalArgumentException("Only <null>, numbers and strings values can be used in the 'where' clause")
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}
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}
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override fun addCondition(condition: Condition) {
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throw IllegalStateException("Can't add a nested condition to the sql 'eq'")
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}
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override fun toString(): String {
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return when (value) {
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null -> "$column is null"
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is String -> "$column = '$value'"
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else -> "$column = $value"
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}
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}
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}
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class SqlSelectBuilder {
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private val columns = mutableListOf<String>()
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private lateinit var table: String
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private var condition: Condition? = null
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fun select(vararg columns: String) {
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if (columns.isEmpty()) {
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throw IllegalArgumentException("At least one column should be defined")
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}
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if (this.columns.isNotEmpty()) {
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throw IllegalStateException("Detected an attempt to re-define columns to fetch. Current columns list: "
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+ "${this.columns}, new columns list: $columns")
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}
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this.columns.addAll(columns)
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}
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fun from(table: String) {
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this.table = table
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}
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fun where(initializer: Condition.() -> Unit) {
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condition = And().apply(initializer)
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}
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fun build(): String {
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if (!::table.isInitialized) {
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throw IllegalStateException("Failed to build an sql select - target table is undefined")
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}
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return toString()
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}
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override fun toString(): String {
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val columnsToFetch =
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if (columns.isEmpty()) {
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"*"
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} else {
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columns.joinToString(", ")
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}
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val conditionString =
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if (condition == null) {
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""
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} else {
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" where $condition"
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}
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return "select $columnsToFetch from $table$conditionString"
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}
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}
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fun query(initializer: SqlSelectBuilder.() -> Unit): SqlSelectBuilder {
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return SqlSelectBuilder().apply(initializer)
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}
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@ -0,0 +1,74 @@
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package com.baeldung.kotlin.dsl
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import org.assertj.core.api.Assertions.assertThat
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import org.junit.Test
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import java.lang.Exception
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class SqlDslTest {
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@Test
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fun `when no columns are specified then star is used`() {
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doTest("select * from table1") {
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from ("table1")
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}
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}
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@Test
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fun `when no condition is specified then correct query is built`() {
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doTest("select column1, column2 from table1") {
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select("column1", "column2")
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from ("table1")
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}
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}
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@Test(expected = Exception::class)
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fun `when no table is specified then an exception is thrown`() {
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query {
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select("column1")
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}.build()
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}
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@Test
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fun `when a list of conditions is specified then it's respected`() {
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doTest("select * from table1 where (column3 = 4 and column4 is null)") {
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from ("table1")
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where {
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"column3" eq 4
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"column4" eq null
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}
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}
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}
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@Test
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fun `when 'or' conditions are specified then they are respected`() {
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doTest("select * from table1 where (column3 = 4 or column4 is null)") {
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from ("table1")
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where {
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or {
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"column3" eq 4
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"column4" eq null
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}
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}
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}
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}
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@Test
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fun `when either 'and' or 'or' conditions are specified then they are respected`() {
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doTest("select * from table1 where ((column3 = 4 or column4 is null) and column5 = 42)") {
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from ("table1")
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where {
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and {
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or {
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"column3" eq 4
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"column4" eq null
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}
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"column5" eq 42
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}
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}
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}
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}
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private fun doTest(expected: String, sql: SqlSelectBuilder.() -> Unit) {
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assertThat(query(sql).build()).isEqualTo(expected)
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}
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}
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