Introduce special str function implementation for T-SQL

documentation/src/test/java/org/hibernate/userguide/hql/HQLTest.java

@@ -1459,6 +1459,7 @@ public class HQLTest extends BaseEntityManagerFunctionalTestCase {
 	public void test_hql_str_function_example_sql_server() {
 		doInJPA( this::entityManagerFactory, entityManager -> {
 			//tag::hql-str-function-example[]
+			// Special SQL Server function "str" that converts floats
 			List<String> timestamps = entityManager.createQuery(
 				"select str( cast(duration as float) / 60, 4, 2 ) " +
 				"from Call c ", String.class )

hibernate-core/src/main/java/org/hibernate/dialect/AbstractTransactSQLDialect.java

@@ -8,6 +8,8 @@ package org.hibernate.dialect;
 
 import org.hibernate.LockMode;
 import org.hibernate.LockOptions;
+import org.hibernate.dialect.function.CastStrEmulation;
+import org.hibernate.dialect.function.TransactSQLStrFunction;
 import org.hibernate.query.NullOrdering;
 import org.hibernate.boot.TempTableDdlTransactionHandling;
 import org.hibernate.cfg.Environment;
@@ -116,6 +118,7 @@ public abstract class AbstractTransactSQLDialect extends Dialect {
 
 		queryEngine.getSqmFunctionRegistry().register( "least", new CaseLeastGreatestEmulation( true ) );
 		queryEngine.getSqmFunctionRegistry().register( "greatest", new CaseLeastGreatestEmulation( false ) );
+		queryEngine.getSqmFunctionRegistry().register( "str", new TransactSQLStrFunction() );
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/dialect/function/CastStrEmulation.java

@@ -10,6 +10,8 @@ import org.hibernate.metamodel.model.domain.AllowableFunctionReturnType;
 import org.hibernate.query.spi.QueryEngine;
 import org.hibernate.query.sqm.function.AbstractSqmFunctionDescriptor;
 import org.hibernate.query.sqm.function.SelfRenderingSqmFunction;
+import org.hibernate.query.sqm.produce.function.ArgumentsValidator;
+import org.hibernate.query.sqm.produce.function.FunctionReturnTypeResolver;
 import org.hibernate.query.sqm.produce.function.StandardArgumentsValidators;
 import org.hibernate.query.sqm.produce.function.StandardFunctionReturnTypeResolvers;
 import org.hibernate.query.sqm.tree.SqmTypedNode;
@@ -35,13 +37,20 @@ public class CastStrEmulation
 		);
 	}
 
+	protected CastStrEmulation(
+			String name,
+			ArgumentsValidator argumentsValidator,
+			FunctionReturnTypeResolver returnTypeResolver) {
+		super( name, argumentsValidator, returnTypeResolver );
+	}
+
 	@Override
 	protected <T> SelfRenderingSqmFunction<T> generateSqmFunctionExpression(
 			List<? extends SqmTypedNode<?>> arguments,
 			AllowableFunctionReturnType<T> impliedResultType,
 			QueryEngine queryEngine,
 			TypeConfiguration typeConfiguration) {
-		SqmTypedNode<?> argument = arguments.get(0);
+		final SqmTypedNode<?> argument = arguments.get( 0 );
 		return queryEngine.getSqmFunctionRegistry().findFunctionDescriptor( "cast" )
 				.generateSqmExpression(
 						asList(

hibernate-core/src/main/java/org/hibernate/dialect/function/TransactSQLStrFunction.java

@@ -0,0 +1,71 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
+ */
+package org.hibernate.dialect.function;
+
+import java.util.List;
+
+import org.hibernate.metamodel.model.domain.AllowableFunctionReturnType;
+import org.hibernate.query.spi.QueryEngine;
+import org.hibernate.query.sqm.function.FunctionRenderingSupport;
+import org.hibernate.query.sqm.function.SelfRenderingSqmFunction;
+import org.hibernate.query.sqm.produce.function.StandardArgumentsValidators;
+import org.hibernate.query.sqm.produce.function.StandardFunctionReturnTypeResolvers;
+import org.hibernate.query.sqm.tree.SqmTypedNode;
+import org.hibernate.sql.ast.SqlAstTranslator;
+import org.hibernate.sql.ast.spi.SqlAppender;
+import org.hibernate.sql.ast.tree.SqlAstNode;
+import org.hibernate.type.StandardBasicTypes;
+import org.hibernate.type.spi.TypeConfiguration;
+
+/**
+ * A special function that renders to the T-SQL "str" function if more than a single argument is given,
+ * otherwise renders a cast expression like {@link CastStrEmulation}.
+ *
+ * @author Christian Beikov
+ */
+public class TransactSQLStrFunction extends CastStrEmulation implements FunctionRenderingSupport {
+
+	public TransactSQLStrFunction() {
+		super(
+				"str",
+				StandardArgumentsValidators.between( 1, 3 ),
+				StandardFunctionReturnTypeResolvers.invariant( StandardBasicTypes.STRING )
+		);
+	}
+
+	@Override
+	protected <T> SelfRenderingSqmFunction<T> generateSqmFunctionExpression(
+			List<? extends SqmTypedNode<?>> arguments,
+			AllowableFunctionReturnType<T> impliedResultType,
+			QueryEngine queryEngine,
+			TypeConfiguration typeConfiguration) {
+		if ( arguments.size() == 1 ) {
+			return super.generateSqmFunctionExpression( arguments, impliedResultType, queryEngine, typeConfiguration );
+		}
+
+		return new SelfRenderingSqmFunction<>(
+				this,
+				this,
+				arguments,
+				impliedResultType,
+				getReturnTypeResolver(),
+				queryEngine.getCriteriaBuilder(),
+				getName()
+		);
+	}
+
+	@Override
+	public void render(SqlAppender sqlAppender, List<SqlAstNode> arguments, SqlAstTranslator<?> walker) {
+		sqlAppender.appendSql( "str(" );
+		arguments.get( 0 ).accept( walker );
+		for ( int i = 1; i < arguments.size(); i++ ) {
+			sqlAppender.appendSql( ", " );
+			arguments.get( i ).accept( walker );
+		}
+		sqlAppender.appendSql( ')' );
+	}
+}