[英]Entity Framework : deleting child entities
我正在使用EF,但是我禁用了延遲加載。 相反,我使用的是急切的加載,因此我創建了自己的服務:
/// <summary>
/// Generic service for entity framework
/// </summary>
/// <typeparam name="T">An entity model</typeparam>
public class Service<T> : IService<T> where T : class
{
// Create our private properties
private readonly DbContext _context;
private readonly DbSet<T> _dbEntitySet;
/// <summary>
/// Default constructor
/// </summary>
/// <param name="context">The database context</param>
public Service(DbContext context)
{
// Assign our context and entity set
_context = context ?? throw new ArgumentNullException("context");
_dbEntitySet = context.Set<T>();
}
/// <summary>
/// Gets all the entities
/// </summary>
/// <param name="includes">Option includes for eager loading</param>
/// <returns></returns>
public IQueryable<T> List(params string[] includes)
{
// Create a query
IQueryable<T> query = _dbEntitySet;
// For each include, append to our query
if (includes != null)
foreach (var include in includes)
query = query.Include(include);
// Return our query
return query;
}
/// <summary>
/// Creates an entity
/// </summary>
/// <param name="model"></param>
public void Create(T model) => _dbEntitySet.Add(model);
/// <summary>
/// Updates an entity
/// </summary>
/// <param name="model"></param>
public void Update(T model) => _context.Entry<T>(model).State = EntityState.Modified;
/// <summary>
/// Removes an entity
/// </summary>
/// <param name="model"></param>
public void Remove(T model) => _context.Entry<T>(model).State = EntityState.Deleted;
/// <summary>
/// Saves the database context changes
/// </summary>
/// <returns></returns>
public async Task SaveChangesAsync()
{
try
{
// Save the changes to the database
await _context.SaveChangesAsync();
}
catch (DbEntityValidationException ex)
{
// Retrieve the error messages as a list of strings.
var errorMessages = ex.EntityValidationErrors.SelectMany(x => x.ValidationErrors).Select(x => x.ErrorMessage);
// Join the list to a single string.
var fullErrorMessage = string.Join("; ", errorMessages);
// Combine the original exception message with the new one.
var exceptionMessage = string.Concat(ex.Message, " The validation errors are: ", fullErrorMessage);
// Throw a new DbEntityValidationException with the improved exception message.
throw new DbEntityValidationException(exceptionMessage, ex.EntityValidationErrors);
}
catch (DbUpdateException ex)
{
throw;
}
}
/// <summary>
/// Executes a stored procedure in sql
/// </summary>
/// <param name="procedure">The name of the sproc</param>
/// <param name="parameters">the sql params for the sproc</param>
/// <returns></returns>
public DbRawSqlQuery<T> ExecuteProcedure(string procedure, List<SqlParameter> parameters)
{
var results = _context.Database.SqlQuery<T>($"exec {procedure} { CreateQueryStringFromParams(parameters) }");
return results;
}
/// <summary>
/// Dispose
/// </summary>
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
/// <summary>
/// Creates the input string to run sprocs in sql with EF by converting the sql params into a nice string
/// </summary>
/// <param name="parameters"></param>
/// <returns></returns>
private static string CreateQueryStringFromParams(IEnumerable<SqlParameter> parameters)
{
var response = "";
var list = parameters as IList<SqlParameter> ?? parameters.ToList();
var length = list.Count;
for (var i = 0; i < length; i++)
{
response += $"{list[i].ParameterName}=\"{list[i].Value}\"";
if (i != length - 1)
response += ", ";
}
return response;
}
/// <summary>
/// Disposes of any attached resources
/// </summary>
/// <param name="disposing">A boolean indicating whether the object is being disposed</param>
protected virtual void Dispose(bool disposing)
{
// If we are disposing, dispose of our context
if (disposing)
_context.Dispose();
}
}
然后,每個服務都將繼承此類:
/// <summary>
/// Handles all Group related methods
/// </summary>
public class GroupService : Service<Group>, IGroupService
{
/// <summary>
/// The default constructor
/// </summary>
/// <param name="unitOfWork"></param>
public GroupService(DbContext context) : base(context)
{
}
/// <summary>
/// Lists groups by category
/// </summary>
/// <param name="categoryId">The id of the category</param>
/// <param name="includes"></param>
/// <returns></returns>
public IQueryable<Group> List(int categoryId, params string[] includes) => List(includes).Where(m => m.CategoryId == categoryId);
/// <summary>
/// Gets a single Group by id
/// </summary>
/// <param name="id">The id of the Group</param>
/// <returns></returns>
public async Task<Group> GetAsync(int id, params string[] includes) => await List(includes).Where(model => model.Id == id).SingleOrDefaultAsync();
}
每個“實體”都有一個與此GroupService相似的類。 我也為每種實體類型提供了提供程序 ,這是我的刪除方法:
/// <summary>
/// Delete a Group
/// </summary>
/// <param name="id">The Group id</param>
/// <returns></returns>
public async Task<bool> DeleteAsync(int id)
{
// Get our model
var model = await _service.GetAsync(id, "Questions");
// For each question, remove from the database
if (model.Questions != null)
foreach (var question in model.Questions.ToList())
if (!await _questionProvider.Value.DeleteAsync(question.Id, false))
throw new Exception("Failed to delete the questions");
// Update our Questions
model.Questions = null;
// Save our model
_service.Remove(model);
// Save the database changes
await _service.SaveChangesAsync();
// Return true
return true;
}
如您所見,我只是撤回了問題。
如果有問題,那么我將調用questionProvider的 delete方法,該方法非常相似:
/// <summary>
/// Delete a question
/// </summary>
/// <param name="id">The question id</param>
/// <param name="saveChanges">Saves the changes to the database after the delete (default true)</param>
/// <returns></returns>
public async Task<bool> DeleteAsync(int id, bool saveChanges = true)
{
// Get our model
var model = await _service.GetAsync(id, "Answers");
// For each answer, delete from the database
if (model.Answers != null)
foreach (var answer in model.Answers.ToList())
if (!await _answerProvider.Value.DeleteAsync(answer.Id, false))
throw new Exception("Failed to delete the answers");
// Update our Answers
model.Answers = null;
// Save our model
_service.Remove(model);
// Save the database changes
if (saveChanges) await _service.SaveChangesAsync();
// Return true
return true;
}
如您所見,在刪除所有子級之前,我不會保存上下文更改。 現在,我必須指出,我不是要直接從父母那里移除孩子。 相反,我是從其自己的集合中刪除該實體,然后將該屬性設置為null。 完成所有操作后,我保存更改,但出現此錯誤:
操作失敗:由於一個或多個外鍵屬性不可為空,因此無法更改該關系。 對關系進行更改時,相關的外鍵屬性將設置為空值。 如果外鍵不支持空值,則必須定義新的關系,必須為外鍵屬性分配另一個非空值,或者必須刪除不相關的對象。
有誰知道我可以用與我嘗試實現的方法類似的方法刪除實體?
在閱讀了其他一些有類似問題的人之后,這個問題很容易解決。 我只是從以下位置更改了Service.cs中的一行代碼:
public void Remove(T model) => _context.Entry<T>(model).State = EntityState.Deleted;
至:
public void Remove(T model) => _dbEntitySet.Remove(model);
那行得通。
更新
我還發現,急切的負載需要包括將受到影響的所有導航屬性。 所以,如果我要刪除的有答案和答案的問題中有公式 ,在獲取調用必須是:
var model = await _service.GetAsync(id, "Answers.Formulas");
如果不包括在內,則會出現錯誤。
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