diff --git a/core-kotlin/src/main/kotlin/com/baeldung/kotlin/dsl/SqlDsl.kt b/core-kotlin/src/main/kotlin/com/baeldung/kotlin/dsl/SqlDsl.kt new file mode 100644 index 0000000000..5296d301a3 --- /dev/null +++ b/core-kotlin/src/main/kotlin/com/baeldung/kotlin/dsl/SqlDsl.kt @@ -0,0 +1,114 @@ +package com.baeldung.kotlin.dsl + +abstract class Condition { + + fun and(initializer: Condition.() -> Unit) { + addCondition(And().apply(initializer)) + } + + fun or(initializer: Condition.() -> Unit) { + addCondition(Or().apply(initializer)) + } + + infix fun String.eq(value: Any?) { + addCondition(Eq(this, value)) + } + + protected abstract fun addCondition(condition: Condition) +} + +open class CompositeCondition(private val sqlOperator: String) : Condition() { + private val conditions = mutableListOf() + + override fun addCondition(condition: Condition) { + conditions += condition + } + + override fun toString(): String { + return if (conditions.size == 1) { + conditions.first().toString() + } else { + conditions.joinToString(prefix = "(", postfix = ")", separator = " $sqlOperator ") { + "$it" + } + } + } +} + +class And : CompositeCondition("and") + +class Or : CompositeCondition("or") + +class Eq(private val column: String, private val value: Any?) : Condition() { + + init { + if (value != null && value !is Number && value !is String) { + throw IllegalArgumentException("Only , numbers and strings values can be used in the 'where' clause") + } + } + + override fun addCondition(condition: Condition) { + throw IllegalStateException("Can't add a nested condition to the sql 'eq'") + } + + override fun toString(): String { + return when (value) { + null -> "$column is null" + is String -> "$column = '$value'" + else -> "$column = $value" + } + } +} + +class SqlSelectBuilder { + + private val columns = mutableListOf() + private lateinit var table: String + private var condition: Condition? = null + + fun select(vararg columns: String) { + if (columns.isEmpty()) { + throw IllegalArgumentException("At least one column should be defined") + } + if (this.columns.isNotEmpty()) { + throw IllegalStateException("Detected an attempt to re-define columns to fetch. Current columns list: " + + "${this.columns}, new columns list: $columns") + } + this.columns.addAll(columns) + } + + fun from(table: String) { + this.table = table + } + + fun where(initializer: Condition.() -> Unit) { + condition = And().apply(initializer) + } + + fun build(): String { + if (!::table.isInitialized) { + throw IllegalStateException("Failed to build an sql select - target table is undefined") + } + return toString() + } + + override fun toString(): String { + val columnsToFetch = + if (columns.isEmpty()) { + "*" + } else { + columns.joinToString(", ") + } + val conditionString = + if (condition == null) { + "" + } else { + " where $condition" + } + return "select $columnsToFetch from $table$conditionString" + } +} + +fun query(initializer: SqlSelectBuilder.() -> Unit): SqlSelectBuilder { + return SqlSelectBuilder().apply(initializer) +} \ No newline at end of file diff --git a/core-kotlin/src/test/kotlin/com/baeldung/kotlin/dsl/SqlDslTest.kt b/core-kotlin/src/test/kotlin/com/baeldung/kotlin/dsl/SqlDslTest.kt new file mode 100644 index 0000000000..55ae44e4dc --- /dev/null +++ b/core-kotlin/src/test/kotlin/com/baeldung/kotlin/dsl/SqlDslTest.kt @@ -0,0 +1,74 @@ +package com.baeldung.kotlin.dsl + +import org.assertj.core.api.Assertions.assertThat +import org.junit.Test +import java.lang.Exception + +class SqlDslTest { + + @Test + fun `when no columns are specified then star is used`() { + doTest("select * from table1") { + from ("table1") + } + } + + @Test + fun `when no condition is specified then correct query is built`() { + doTest("select column1, column2 from table1") { + select("column1", "column2") + from ("table1") + } + } + + @Test(expected = Exception::class) + fun `when no table is specified then an exception is thrown`() { + query { + select("column1") + }.build() + } + + @Test + fun `when a list of conditions is specified then it's respected`() { + doTest("select * from table1 where (column3 = 4 and column4 is null)") { + from ("table1") + where { + "column3" eq 4 + "column4" eq null + } + } + } + + @Test + fun `when 'or' conditions are specified then they are respected`() { + doTest("select * from table1 where (column3 = 4 or column4 is null)") { + from ("table1") + where { + or { + "column3" eq 4 + "column4" eq null + } + } + } + } + + @Test + fun `when either 'and' or 'or' conditions are specified then they are respected`() { + doTest("select * from table1 where ((column3 = 4 or column4 is null) and column5 = 42)") { + from ("table1") + where { + and { + or { + "column3" eq 4 + "column4" eq null + } + "column5" eq 42 + } + } + } + } + + private fun doTest(expected: String, sql: SqlSelectBuilder.() -> Unit) { + assertThat(query(sql).build()).isEqualTo(expected) + } +} \ No newline at end of file