#48 Add support for CASE expression (#122)

src/dml/case-expression.ts

@@ -0,0 +1,24 @@
+import { Expression } from '../expression';
+
+export interface CaseCondition {
+	when: Expression;
+	then: Expression;
+}
+
+export interface CaseExpressionInterface {
+	value?: Expression;
+	case: CaseCondition[];
+	else?: Expression;
+}
+
+export class CaseExpression implements CaseExpressionInterface {
+	value?: Expression;
+	case: CaseCondition[];
+	else?: Expression;
+
+	public constructor(expr: CaseExpressionInterface) {
+		this.value = expr.value;
+		this.case = expr.case;
+		this.else = expr.else;
+	}
+}

src/dml/index.ts

@@ -1,6 +1,7 @@
 export { DatabaseQueryBuilder } from './query-builder';
 export { QueryRepository, QueryRepositoryOptions } from './query-repository';
 
+export * from './case-expression';
 export * from './delete';
 export * from './insert';
 export * from './join';

src/dml/query-builder.ts

@@ -36,6 +36,7 @@ import {
 } from '../functions/function-token';
 import { Subquery } from './subquery';
 import { KeyValExpression } from '../expression/key-val-expression';
+import { CaseExpression } from './case-expression';
 
 export class DatabaseQueryBuilder extends StatementBuilder {
 	// ------------------------------------------------------------------------
@@ -81,6 +82,9 @@ export class DatabaseQueryBuilder extends StatementBuilder {
 			else if (expr instanceof Subquery) {
 				this.subquery(expr);
 			}
+			else if (expr instanceof CaseExpression) {
+				this.caseExpression(expr);
+			}
 			else {
 				this.keyValueExpression(expr as KeyValExpression);
 			}
@@ -97,6 +101,33 @@ export class DatabaseQueryBuilder extends StatementBuilder {
 		this.sql.trimEnd(' ');
 	}
 
+	public caseExpression(expr: CaseExpression) {
+		this.sql.openParens();
+		this.sql.append('CASE ');
+
+		if (expr.value) {
+			this.expression(expr.value);
+			this.sql.space();
+		}
+
+		for (const condition of expr.case) {
+			this.sql.append('WHEN ');
+			this.expression(condition.when);
+			this.sql.append('THEN ');
+			this.expression(condition.then);
+		}
+
+		if (expr.else) {
+			this.sql.append('ELSE ');
+			this.expression(expr.else);
+		}
+
+		this.sql.append('END');
+
+		this.sql.closeParens();
+		this.sql.trimEnd(' ');
+	}
+
 	public rawExpression(expr: RawExpressionToken) {
 		this.sql.append(expr.sql);
 

src/expression/simple-expression.ts

@@ -4,6 +4,7 @@ import { Literal } from './literal';
 import { DatabaseFunctionToken } from '../functions';
 import { MathToken } from './math';
 import { RawExpressionToken } from './raw';
+import { CaseExpression } from '../dml/case-expression';
 
 export type SimpleExpression =
 	| Literal
@@ -12,4 +13,5 @@ export type SimpleExpression =
 	| MathToken
 	| DatabaseFunctionToken
 	| Subquery
+	| CaseExpression
 	| SimpleExpression[];

test/spec/dml/query-builder.spec.ts

@@ -23,7 +23,7 @@ import {
 	raw,
 	times,
 } from '../../../src/expression';
-import { Subquery } from '../../../src/dml';
+import { CaseExpression, Subquery } from '../../../src/dml';
 
 describe('Query Builder', () => {
 	describe('Select', () => {
@@ -185,6 +185,55 @@ describe('Query Builder', () => {
 			);
 		});
 
+		it('can select case expression', () => {
+			const { sql, params } = new DatabaseQueryBuilder()
+				.select({
+					columns: [
+						{
+							query: new CaseExpression({
+								case: [
+									{ when: [4, gt(5)], then: 'four' },
+									{ when: [5, gt(4)], then: 'five' },
+								],
+								else: 'hmm',
+							}),
+							as: 'val',
+						},
+					],
+				})
+				.toDatabaseQuery();
+
+			expect(sql).toEqual(
+				'SELECT (CASE WHEN (? > ?) THEN ? WHEN (? > ?) THEN ? ELSE ? END) AS "val"'
+			);
+			expect(params).toEqual([4, 5, 'four', 5, 4, 'five', 'hmm']);
+		});
+
+		it('can select case expression with value', () => {
+			const { sql, params } = new DatabaseQueryBuilder()
+				.select({
+					columns: [
+						{
+							query: new CaseExpression({
+								value: 5,
+								case: [
+									{ when: 4, then: 'four' },
+									{ when: 5, then: 'five' },
+								],
+								else: 'hmm',
+							}),
+							as: 'val',
+						},
+					],
+				})
+				.toDatabaseQuery();
+
+			expect(sql).toEqual(
+				'SELECT (CASE ?  WHEN ? THEN ? WHEN ? THEN ? ELSE ? END) AS "val"'
+			);
+			expect(params).toEqual([5, 4, 'four', 5, 'five', 'hmm']);
+		});
+
 		it('can left join', () => {
 			const { sql } = new DatabaseQueryBuilder()
 				.select({