#3173 - BeanSet lazy loading / Too many DataSource connections used

- The error reported was that a DataSource connection pool maxed out
- The symptom was that there was an additional lazy loading queries invoked via the hashCode/equals implementation of ManyToMany Set.
- The fix is for BeanSet init() to lazy load with onlyIds = false, that avoids the extra lazy loading query from being executed

ebean-api/src/main/java/io/ebean/common/BeanSet.java

@@ -136,7 +136,7 @@ private void init() {
         if (disableLazyLoad) {
           set = new LinkedHashSet<>();
         } else {
-          lazyLoadCollection(true);
+          lazyLoadCollection(false);
         }
       }
     } finally {

ebean-test/src/test/java/org/tests/sets/M2MDepart.java

@@ -0,0 +1,38 @@
+package org.tests.sets;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+import javax.persistence.ManyToMany;
+import java.util.*;
+
+@Entity
+public class M2MDepart {
+
+  @Id
+  private UUID id;
+
+  private final String name;
+
+  @ManyToMany
+  private final Set<M2MEmp> employees = new LinkedHashSet<>();
+
+  public M2MDepart(String name) {
+    this.name = name;
+  }
+
+  public void addEmployee(M2MEmp employee) {
+    this.employees.add(employee);
+  }
+
+  public UUID getId() {
+    return id;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public Set<M2MEmp> employees() {
+    return employees;
+  }
+}

ebean-test/src/test/java/org/tests/sets/M2MEmp.java

@@ -0,0 +1,61 @@
+package org.tests.sets;
+
+import javax.persistence.*;
+import java.util.HashSet;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+
+@Entity
+public class M2MEmp {
+
+  @Id
+  private UUID id;
+
+  private final String code;
+
+  private String name;
+
+  @ManyToMany
+  @JoinTable(name="m2m_dept_emp",
+          joinColumns=
+          @JoinColumn(name="employee_id", referencedColumnName="id"),
+          inverseJoinColumns=
+          @JoinColumn(name="department_id", referencedColumnName="id")
+  )
+  private final Set<M2MDepart> departments = new HashSet<>();
+
+  public M2MEmp(String name, String code) {
+    this.name = name;
+    this.code = code;
+  }
+
+  public UUID getId() {
+    return id;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public String getCode() {
+    return code;
+  }
+
+  public Set<M2MDepart> getDepartments() {
+    return departments;
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) return true;
+    if (o == null || getClass() != o.getClass()) return false;
+    M2MEmp employee = (M2MEmp) o;
+    return Objects.equals(code, employee.code);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(code);
+  }
+}

ebean-test/src/test/java/org/tests/sets/TestM2MSet.java

@@ -0,0 +1,31 @@
+package org.tests.sets;
+
+import io.ebean.DB;
+import io.ebean.test.LoggedSql;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class TestM2MSet {
+
+  @Test
+  void lazyLoadM2M_when_setWithHashCode_expect_selectProperties() {
+    final M2MDepart department = new M2MDepart("Test");
+    final M2MEmp employee = new M2MEmp("Test", "Code");
+    DB.save(employee);
+    department.addEmployee(employee);
+    DB.save(department);
+
+    LoggedSql.start();
+    DB.find(M2MDepart.class, department.getId())
+      .employees()
+      .forEach(e -> assertThat(e.getName()).isNotNull());
+
+    List<String> sql = LoggedSql.stop();
+    assertThat(sql).hasSize(2);
+    assertThat(sql.get(0)).contains("select t0.id, t0.name from m2_mdepart t0 where t0.id = ?");
+    assertThat(sql.get(1)).contains("select int_.m2_mdepart_id, t0.id, t0.code, t0.name from m2_memp t0 left join m2_mdepart_memp int_ on int_.m2_memp_id = t0.id where");
+  }
+}