How to Check for Entity Changes

• The session's advanced property HasChanged indicates whether the specified entity was added, modified, or deleted within the session.

• Note: The HasChanged property is cleared after calling SaveChanges().

using (var session = store.OpenSession())
{
    // Store a new entity within the session
    // =====================================
    
    Employee employee = new Employee {FirstName = "John", LastName = "Doe"};
    session.Store(employee, "employees/1-A");
    
    // 'HasChanged' will be TRUE 
    Assert.True(session.Advanced.HasChanged(employee));
    
    // 'HasChanged' will reset to FALSE after saving changes 
    session.SaveChanges();
    Assert.False(session.Advanced.HasChanged(employee));
    
    // Load & modify entity within the session
    // =======================================
    
    employee = session.Load<Employee>("employees/1-A");
    Assert.False(session.Advanced.HasChanged(employee)); // FALSE
    
    employee.LastName = "Brown";
    Assert.True(session.Advanced.HasChanged(employee)); // TRUE
    
    session.SaveChanges();
    Assert.False(session.Advanced.HasChanged(employee)); // FALSE
}

• Use the session's advanced method WhatChangedFor() to get all changes made to the specified entity
  within the session.

• Details will include:

  • The name and path of the changed field
  • Its old and new values
  • The type of change

Example I

using (var session = store.OpenSession())
{
    // Store (add) a new entity, it will be tracked by the session
    Employee employee = new Employee {FirstName = "John", LastName = "Doe"};
    session.Store(employee, "employees/1-A");

    // Get the changes for the entity in the session
    // Call 'WhatChangedFor', pass the entity object in the param
    DocumentsChanges[] changesForEmployee = session.Advanced.WhatChangedFor(employee);
    Assert.Equal(changesForEmployee.Length, 1); // a single change for this entity (adding)
    
    // Get the change type
    DocumentsChanges.ChangeType changeType = changesForEmployee[0].Change;
    Assert.Equal(changeType, DocumentsChanges.ChangeType.DocumentAdded);
    
    session.SaveChanges();
}

Example II

using (var session = store.OpenSession())
{
    
    // Load the entity, it will be tracked by the session
    Employee employee = session.Load<Employee>("employees/1-A");
    
    // Modify the entity
    employee.FirstName = "Jim";
    employee.LastName = "Brown";
    
    // Get the changes for the entity in the session
    // Call 'WhatChangedFor', pass the entity object in the param
    DocumentsChanges[] changesForEmployee = session.Advanced.WhatChangedFor(employee);
   
    Assert.Equal(changesForEmployee[0].FieldName, "FirstName");                           // Field name
    Assert.Equal(changesForEmployee[0].FieldNewValue, "Jim");                             // New value
    Assert.Equal(changesForEmployee[0].Change, DocumentsChanges.ChangeType.FieldChanged); // Change type
    
    Assert.Equal(changesForEmployee[1].FieldName, "LastName");
    Assert.Equal(changesForEmployee[1].FieldNewValue, "Brown");
    Assert.Equal(changesForEmployee[1].Change, DocumentsChanges.ChangeType.FieldChanged);
    
    session.SaveChanges();
}

// HasChanged
bool HasChanged(object entity);

// WhatChangedFor
DocumentsChanges[] WhatChangedFor(object entity);

public class DocumentsChanges
{
    public object FieldOldValue { get; set; }  // Previous field value
    public object FieldNewValue { get; set; }  // Current field value
    public ChangeType Change { get; set; }     // Type of change that occurred
    public string FieldName { get; set; }      // Name of field on which the change occurred
    public string FieldPath { get; set; }      // Path of field on which the change occurred
    public string FieldFullName { get; }       // Path + Name of field on which the change occurred
}

public enum ChangeType
{
    DocumentDeleted,
    DocumentAdded,
    FieldChanged,
    NewField,
    RemovedField,
    ArrayValueChanged,
    ArrayValueAdded,
    ArrayValueRemoved
}