Insert should work without giving any explicit assignment/variables

src/main/java/org/springframework/data/r2dbc/core/DefaultDatabaseClient.java

@@ -1044,10 +1044,6 @@ public Mono<Void> then() {
 
 		private <R> FetchSpec<R> exchange(BiFunction<Row, RowMetadata, R> mappingFunction) {
 
-			if (this.byName.isEmpty()) {
-				throw new IllegalStateException("Insert fields is empty!");
-			}
-
 			StatementMapper mapper = dataAccessStrategy.getStatementMapper();
 			StatementMapper.InsertSpec insert = mapper.createInsert(this.table);
 

src/main/java/org/springframework/data/r2dbc/core/DefaultStatementMapper.java

@@ -159,10 +159,6 @@ private PreparedOperation<Insert> getMappedObject(InsertSpec insertSpec,
 
 		Bindings bindings;
 
-		if (boundAssignments.getAssignments().isEmpty()) {
-			throw new IllegalStateException("INSERT contains no values");
-		}
-
 		bindings = boundAssignments.getBindings();
 
 		InsertBuilder.InsertIntoColumnsAndValues insertBuilder = StatementBuilder.insert(table);

src/test/java/org/springframework/data/r2dbc/core/DefaultDatabaseClientUnitTests.java

@@ -249,6 +249,22 @@ public void insertShouldAcceptSettableValue() {
 		verify(statement).bindNull(1, Integer.class);
 	}
 
+	@Test
+	public void insertShouldWorkWithoutValues() {
+
+		Statement statement = mockStatementFor("INSERT INTO id_only VALUES ()");
+		DatabaseClient databaseClient = databaseClientBuilder.build();
+
+		databaseClient.insert().into("id_only") //
+				.then() //
+				.as(StepVerifier::create) //
+				.verifyComplete();
+
+		verify(statement).returnGeneratedValues();
+		verify(statement).execute();
+		verifyNoMoreInteractions(statement);
+	}
+
 	@Test // gh-128
 	public void executeShouldBindNamedValuesByIndex() {
 

src/test/java/org/springframework/data/r2dbc/repository/AbstractR2dbcRepositoryIntegrationTests.java

@@ -61,7 +61,7 @@ public abstract class AbstractR2dbcRepositoryIntegrationTests extends R2dbcInteg
 
 	@Autowired private LegoSetRepository repository;
 	@Autowired private ConnectionFactory connectionFactory;
-	private JdbcTemplate jdbc;
+	protected JdbcTemplate jdbc;
 
 	@Before
 	public void before() {

src/test/java/org/springframework/data/r2dbc/repository/H2R2dbcRepositoryIntegrationTests.java

@@ -16,24 +16,33 @@
 package org.springframework.data.r2dbc.repository;
 
 import io.r2dbc.spi.ConnectionFactory;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
 
+import java.util.Arrays;
+
 import javax.sql.DataSource;
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
+import static org.assertj.core.api.Assertions.*;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.ComponentScan.Filter;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.FilterType;
+import org.springframework.data.annotation.Id;
 import org.springframework.data.r2dbc.config.AbstractR2dbcConfiguration;
 import org.springframework.data.r2dbc.repository.config.EnableR2dbcRepositories;
 import org.springframework.data.r2dbc.repository.support.R2dbcRepositoryFactory;
 import org.springframework.data.r2dbc.testing.H2TestSupport;
+import org.springframework.data.relational.core.mapping.Table;
+import org.springframework.data.repository.reactive.ReactiveCrudRepository;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.SpringRunner;
 
@@ -47,10 +56,11 @@
 public class H2R2dbcRepositoryIntegrationTests extends AbstractR2dbcRepositoryIntegrationTests {
 
 	@Autowired private H2LegoSetRepository repository;
+	@Autowired private IdOnlyEntityRepository idOnlyEntityRepository;
 
 	@Configuration
 	@EnableR2dbcRepositories(considerNestedRepositories = true,
-			includeFilters = @Filter(classes = H2LegoSetRepository.class, type = FilterType.ASSIGNABLE_TYPE))
+			includeFilters = @Filter(classes = {H2LegoSetRepository.class, IdOnlyEntityRepository.class}, type = FilterType.ASSIGNABLE_TYPE))
 	static class IntegrationTestConfiguration extends AbstractR2dbcConfiguration {
 
 		@Bean
@@ -60,6 +70,17 @@ public ConnectionFactory connectionFactory() {
 		}
 	}
 
+	interface IdOnlyEntityRepository extends ReactiveCrudRepository<IdOnlyEntity, Integer> {
+	}
+
+	@Getter
+	@Setter
+	@Table("id_only")
+	@NoArgsConstructor
+	static class IdOnlyEntity {
+		@Id Integer id;
+	}
+
 	@Override
 	protected DataSource createDataSource() {
 		return H2TestSupport.createDataSource();
@@ -112,6 +133,18 @@ public void shouldNotReturnUpdateCount() {
 		repository.updateManualAndReturnNothing(42).as(StepVerifier::create).verifyComplete();
 	}
 
+	@Test
+	public void shouldInsertIdOnlyEntity() {
+		this.jdbc.execute("CREATE TABLE ID_ONLY(id serial CONSTRAINT id_only_pk PRIMARY KEY)");
+
+		IdOnlyEntity entity1 = new IdOnlyEntity();
+		idOnlyEntityRepository.saveAll(Arrays.asList(entity1))
+			.as(StepVerifier::create) //
+			.consumeNextWith( actual -> {
+				assertThat(actual.getId()).isNotNull();
+			}).verifyComplete();
+	}
+
 	interface H2LegoSetRepository extends LegoSetRepository {
 
 		@Override