Files to look at:
- frmMain.cs (VB: frmMain.vb)
- SequenceGenerator.cs (VB: SequenceGenerator.vb)
This is a general solution, showing how to use the ExplicitUnitOfWork class to generate sequential numbers that can then be used as user-friendly identifiers in documents, as invoice line numbers, etc. The ExplicitUnitOfWork class is used to ensure that the assignment of the sequential number will be a part of a database transaction that results in the successful saving of the document.
Hence, the current solution will also work in a scenario with high-volume of concurrency transactions.
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Example Code
ExplicitUnitOfWorkDemo/frmMain.cs(vb)
C#using System;
using DevExpress.Xpo;
using DevExpress.XtraEditors;
using System.Collections.Generic;
namespace ExplicitUnitOfWorkDemo {
public partial class frmMain : XtraForm {
public frmMain() {
InitializeComponent();
}
private void btnRecreateAddress_Click(object sender, EventArgs e) {
ViewRecord row = gridView1.GetFocusedRow() as ViewRecord;
if(row == null) return;
long personOid = RecreateAddress(row);
UpdateRows();
gridView1.SetFocusedRowCellValue(colOid, personOid);
}
private static long RecreateAddress(ViewRecord selectedRow) {
long personOid;
using (ExplicitUnitOfWork explicitUnitOfWork = new ExplicitUnitOfWork(DatabaseHelper.DataLayer)) {
//Get selected person object.
Person person = explicitUnitOfWork.GetObjectByKey<Person>(selectedRow["Oid"]);
if(person == null || person.Address == null)
throw new ArgumentNullException("person");
//Remember person key value.
personOid = person.Oid;
Address address = person.Address;
long addressOid = address.Oid;
List<Person> referenceList = new List<Person>(address.Persons);
//Reset references to the Address object.
for (int i = 0; i < referenceList.Count; i++) {
referenceList[i].Address = null;
}
//Delete the Address object.
explicitUnitOfWork.Delete(address);
//Save changes to the database in case of an explicit transaction.
explicitUnitOfWork.FlushChanges();
//Create a new instance of the Address object.
address = DatabaseHelper.CreateNewAddress(explicitUnitOfWork, addressOid);
//Recover references to the Address object.
for (int i = 0; i < referenceList.Count; i++) {
referenceList[i].Address = address;
}
explicitUnitOfWork.CommitChanges();
}
return personOid;
}
private void btnCreatePerson_Click(object sender, EventArgs e) {
CreatePerson();
UpdateRows();
}
private static void CreatePerson() {
long personOid;
using (UnitOfWork uow = new UnitOfWork(DatabaseHelper.SequenceDataLayer)) {
Address address;
using (SequenceGenerator<Address> sg = new SequenceGenerator<Address>(DatabaseHelper.SequenceDataLayer)) {
address = DatabaseHelper.CreateNewAddress(uow, sg.GetNextId());
uow.CommitChanges();
sg.Accept();
}
using (SequenceGenerator<Person> sg = new SequenceGenerator<Person>(DatabaseHelper.SequenceDataLayer)) {
Person person = DatabaseHelper.CreateNewPerson(uow, sg.GetNextId());
personOid = person.Oid;
person.Address = address;
uow.CommitChanges();
sg.Accept();
}
}
}
private void btnCreatePersons_Click(object sender, EventArgs e) {
CreatePersons();
UpdateRows();
}
private static void CreatePersons() {
using (UnitOfWork uow = new UnitOfWork(DatabaseHelper.SequenceDataLayer)) {
List<Address> addressList = new List<Address>();
using (SequenceGenerator<Address> sg = new SequenceGenerator<Address>(DatabaseHelper.SequenceDataLayer)) {
for (int i = 0; i < 10; i++) {
Address address = DatabaseHelper.CreateNewAddress(uow, sg.GetNextId());
addressList.Add(address);
}
uow.CommitChanges();
sg.Accept();
}
using (SequenceGenerator<Person> sg = new SequenceGenerator<Person>(DatabaseHelper.SequenceDataLayer)) {
for (int i = 0; i < 10; i++) {
for (int k = 0; k < 10; k++) {
Person person = DatabaseHelper.CreateNewPerson(uow, sg.GetNextId());
person.Address = addressList[i];
}
}
uow.CommitChanges();
sg.Accept();
}
}
}
private void btnUpdate_Click(object sender, EventArgs e) {
UpdateRows();
}
private void UpdateRows() {
xpView1.TopReturnedRecords = (int)spinEdit1.Value;
xpView1.Reload();
}
private void btnClearDB_Click(object sender, EventArgs e) {
ClearDatabase();
UpdateRows();
}
private static void ClearDatabase() {
using (UnitOfWork uow = new UnitOfWork(DatabaseHelper.DataLayer)) {
XPCollection<Person> personList = new XPCollection<Person>(uow);
XPCollection<Address> addressList = new XPCollection<Address>(uow);
XPCollection<Sequence> sequencList = new XPCollection<Sequence>(uow);
uow.Delete(personList);
uow.Delete(addressList);
uow.Delete(sequencList);
uow.CommitChanges();
}
}
}
}
ExplicitUnitOfWorkDemo/SequenceGenerator.cs(vb)
C#using System;
using DevExpress.Xpo;
using DevExpress.Xpo.Metadata;
using DevExpress.Xpo.DB.Exceptions;
namespace ExplicitUnitOfWorkDemo {
//This class is used to generate sequential numbers for persistent objects.
//Use the GetNextId method to get the next number and the Accept method, to save these changes to the database.
public class SequenceGenerator<T> : IDisposable {
private ExplicitUnitOfWork euow;
private XPClassInfo classInfo;
private Sequence seq;
public SequenceGenerator(IDataLayer dataLayer) {
euow = new ExplicitUnitOfWork(dataLayer);
classInfo = euow.GetClassInfo<T>();
}
public void Accept(){
euow.CommitChanges();
}
public long GetNextId() {
long nextId;
while(true) {
try {
if(seq == null) {
seq = euow.GetObjectByKey<Sequence>(classInfo.FullName, true);
if(seq == null) {
seq = new Sequence(euow);
seq.TypeName = classInfo.FullName;
seq.NextId = 0;
}
}
nextId = seq.NextId;
seq.NextId++;
euow.FlushChanges();
} catch(LockingException) {
seq = null;
continue;
}
break;
}
return nextId;
}
public void Close() {
if(euow != null)
euow.Dispose();
}
void IDisposable.Dispose() {
Close();
}
}
//This persistent class is used to store last sequential number for persistent objects.
public class Sequence : XPBaseObject {
private string typeName;
private long nextId;
public Sequence(Session session)
: base(session) {
}
[Key]
public string TypeName {
get { return typeName; }
set { SetPropertyValue("TypeName", ref typeName, value); }
}
public long NextId {
get { return nextId; }
set { SetPropertyValue("NextId", ref nextId, value); }
}
}
}