I have a simple query:
var car = CarRepository.GetById(1);
var engine = new EngineDto
{
Prop1 = car.Engine.Prop1,
Prop2 = car.Engine.Prop2,
Prop3 = car.Engine.Prop3,
Prop4 = car.Engine.Prop4
}
The issue is the Engine model has more then 50 columns and when I try to get value of Engine model property Entity Framework generate query
SELECT TOP(1) * FROM Engine WHERE ID = <id>
Is there any way to create query for getting only few fields?
Yes, there is a way: don't fetch the complete entity, but use Enumerable.Select to fetch only the data you plan to use.
For this your CarRepository would need a function that return IEnumerable<Car> (or similar IQueryable)
In two steps:
EngineDto engine = CarRepository.QueryCars() // function to fetch IEnumerable<Car>
.Where(car => car.Id == 1)
.Select(car => new EngineDto
{
Prop1 = car.Engine.Prop1,
Prop2 = car.Engine.Prop2,
Prop3 = car.Engine.Prop3,
Prop4 = car.Engine.Prop4,
})
.SingleOrDefault();
If the designer of the CarRepository didn't provide a function that would return a sequence of Cars, then obviously he thought that no one would ever want it. But I'm pretty sure the CarRepository has a function to "fetch all cars"
By the way, as transferring the data from the database to your local process is usually the slower part of your processing, it is always wise to transfer as little data as possible. Try to avoid transferring properties that you didn't plan to use.
Related
I was told to use automapper in the code below. I cannot get clarification for reasons that are too lengthy to go into. What object am I supposed to be mapping to what object? I don't see a "source" object, since the source is the database...
Would really appreciate any help on how to do this with automapper. Note, the actual fields are irrelevant, I need help with the general concept. I do understand how mapping works when mapping from one object to another.
public IQueryable<Object> ReturnDetailedSummaries(long orgId)
{
var summaries = from s in db.ReportSummaries
where s.OrganizationId == orgId
select new SummaryViewModel
{
Id = s.Id,
Name = s.Name,
AuditLocationId = s.AuditLocationId,
AuditLocationName = s.Location.Name,
CreatedOn = s.CreatedOn,
CreatedById = s.CreatedById,
CreatedByName = s.User.Name,
OfficeId = s.OfficeId,
OfficeName = s.Office.Name,
OrganizationId = s.OrganizationId,
OrganizationName = s.Organization.Name,
IsCompleted = s.IsCompleted,
isHidden = s.isHidden,
numberOfItemsInAuditLocations = s.numberOfItemsInAuditLocations,
numberOfLocationsScanned = s.numberOfLocationsScanned,
numberOfItemsScanned = s.numberOfItemsScanned,
numberofDiscrepanciesFound = s.numberofDiscrepanciesFound
};
return summaries;
}
It is a handy and a timesaver, especially if you use a one to one naming between translations layers. Here is how I use it.
For single item
public Domain.Data.User GetUserByUserName(string userName)
{
Mapper.CreateMap<User, Domain.Data.User>();
return (
from s in _dataContext.Users
where s.UserName==userName
select Mapper.Map<User, Domain.Data.User>(s)
).SingleOrDefault();
}
Multiple Items
public List<Domain.Data.User> GetUsersByProvider(int providerID)
{
Mapper.CreateMap<User, Domain.Data.User>();
return (
from s in _dataContext.Users
where s.ProviderID== providerID
select Mapper.Map<User, Domain.Data.User>(s)
).ToList();
}
It looks like you already have a model? SummaryViewModel?
If this isn't the DTO, then presumably you want to do:
Mapper.CreateMap<SummaryViewModel, SummaryViewModelDto>();
SummaryViewModelDto summaryViewModelDto =
Mapper.Map<SummaryViewModel, SummaryViewModelDto>(summaryViewModel);
AutoMapper will copy fields from one object to another, to save you having to do it all manually.
See https://github.com/AutoMapper/AutoMapper/wiki/Getting-started
The source is your entity class ReportSummary, the target is SummaryViewModel:
Mapper.CreateMap<ReportSummary, SummaryViewModel>();
The best way to use AutoMapper in combination with an IQueryable data source is through the Project.To API:
var summaries = db.ReportSummaries.Where(s => s.OrganizationId == orgId)
.Project().To<SummaryViewModel>();
Project.To translates the properties in the target model straight to the selected columns in the generated SQL.
Mapper.Map, on the other hand, only works on in-memory collections, so you can only use it when you first fetch complete ReportSummary objects from the database. (In this case there may not be much of a difference, but in other cases it can be substantial).
I am developing one application in which data is access from edmx entities and from that we have to fill each business entity after retriving data from edmx entity like:-
var tblproducts = tblproductsData
.Select(t => new tblProduct()
{
CategoryID = t.CategoryID,
Description = t.Description,
ID = t.ID,
Image = t.Image,
InsDt = t.InsDt,
Price = t.Price,
Quantity = t.Quantity,
Status = t.Status,
Title = t.Title,
tblCategory = new EFDbFirst.Models.tblCategory()
{
ID = t.tblCategory.ID,
status = t.tblStatus.StatusID,
Title_Category = t.tblCategory.Title_Category
},
tblStatu = new EFDbFirst.Models.tblStatu()
{
StatusDescription = t.tblStatus.StatusDescription
,
StatusID = t.tblStatus.StatusID
}
});
I am fadeup with this because everytime i have to convert one to another while getting data and setting data in db,
Is there any good way to create some common mehod which takes one anonymous type and converts it to another anonymous type.
Thanks in Advance
Your example isn't that clear.
First of all, EF doesn't work with anonymous types inside itself, it works with the EF types you have defined either using edmx file or code first. You can however create anonymous types yourself by defining an Select statement.
E.g:
var products = context.tblProductsData
.Select(r => new { Description = r.Description }); //new without typename is an
//anonymous object
The tblProduct, tblCategory and tblStatu objects, are they EF types? If so, you don't need to write a Select, EF will generate objects for you when you execute it.
E.g:
var products = context.tblProductsData.ToList();
This will automatically generate tblProduct objects for you. When you try to navigate to tblProduct.tblCategory or tblProduct.tblStatu, lazy loading will retrieve them for you. If you want to explicit load them during first query (eager-loading) use the Include function.
E.g:
var products = context.tblProductsData.Include(r => r.tblCategory)
.Include(r => r.tblStatu).ToList();
However if tblProducts, tblCategory and tblStatu is business objects and NOT EF types, there isn't any other way to do this, you have to explicit create them in a Select statement.
I have this entity, want to update using entityframework
EmployeeModel employee = new EmployeeModel
{
Id = 1000, //This one must
FirstName = modifiedValue,
Email = modifiedValue,
LastName = originalValue,
Phone = originalValue
};
Code to update
_db.ObjectStateManager.ChangeObjectState(employee, EntityState.Modified);
_db.SaveChanges();
This is the SQL statement got once updated
Update Employee set Id=1138,FirstName='modifiedValue',Email='modifiedValue',LastName= 'OriginalValue',phone='originalValue' where Id=1138
But I am expecting this
Update Employee set FirstName='modifiedValue', Email='modifiedValue' where Id=1138.
I dont know what I am missing here. Please let me know.
This problem is common when dealing with DTOs. An employee entity is fetched from the database, mapped to a DTO and sent over the wire. The client then modifies this DTO and sends it back to the server.
When you touch (set) a property on an EF entity, EF will assume that the value has been changed. Even if the old value and the new value are exactly the same.
The same problem occurs when you map the DTO to a new Entity and attach it to EF and updating its status to 'Modified'.
Using AutoMapper:
// This will result in the full update statement
var employee = AutoMapper.Mapper.Map<EmployeeDto, Employee>(dto);
// This will result in a smaller update statement (only actual changes)
var employee = dbContext.Employees.Find(dto.Id);
AutoMapper.Mapper.Map(dto, employee);
Or, manually (I would avoid doing this, but just for the sake of completeness):
// This will result in a smaller update statement (only actual changes)
var employee = dbContext.Employees.Find(dto.Id);
if (employee.Email != dto.Email )
employee.Email = dto.Email;
There are probably some other ways for dealing with this problem... but using AutoMapper together with Entity Framework correctly is definitely one of the easiest ways.
This is the solution I got
var entity = _db.CreateObjectSet<Employee>();
entity.Detach(employee);
entity.Attach(employee);
foreach (string modifiedPro in employeeModel.ModifiedProperties){
_db.ObjectStateManager.GetObjectStateEntry(employee).SetModifiedProperty(modifiedPro);}
_db.SaveChanges();
Only modified values in the sql update statement
Update Employee set FirstName='modifiedValue', Email='modifiedValue' where Id=1138.
If anybody knows better answer than this, Please post your suggestions
You can try this way
public update(Person model)
{
// Here model is model return from form on post
var oldobj = db.Person.where(x=>x.ID = model.ID).SingleOrDefault();
var UpdatedObj = (Person) Entity.CheckUpdateObject(oldobj, model);
db.Entry(oldobj).CurrentValues.SetValues(UpdatedObj);
}
public static object CheckUpdateObject(object originalObj, object updateObj)
{
foreach (var property in updateObj.GetType().GetProperties())
{
if (property.GetValue(updateObj, null) == null)
{
property.SetValue(updateObj,originalObj.GetType().GetProperty(property.Name)
.GetValue(originalObj, null));
}
}
return updateObj;
}
Here's what I'd like to do:
var myCustomer = new Customer();
myCustomer.Name = "Bob";
myCustomer.HasAJob = true;
myCustomer.LikesPonies = false;
Then I'd like to pass it into an update method:
public UpdateCustomer(Customer cust)
{
using(var context = dbcontext())
{
var dbCust = context.Customers.FirstOrDefault(c => c.Name == cust.Name);
if(dbCust != null)
{
// Apply values from cust here so I don't have to do this:
dbCust.HasAJob = cust.HasAJob;
dbCust.LikesPonies = cust.LikesPonies
}
context.SaveChanges();
}
}
The reason for this is I'm working in multiple different parts of my application, and/or across DLLs. Is this possible?
EDIT: Found this question to be immensely useful:
Update Row if it Exists Else Insert Logic with Entity Framework
If you are sure that the entity is in the database and you have key you would just Attach the object you have to the context. Note that attached entities are by default in Unchanged state as the assumption is that all the values of properties are the same as in the database. If this is not the case (i.e. values are different) you need to change the state of the entity to modified. Take a look at this blog post: http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx it describes several sceanrios including the one you are asking about.
I'm currently planning on switching my "manual query-writing" code to a nice SQL framework, so I can leave the queries or sql things to the framework, instead of writing the queries myself.
Now I'm wondering how I can get a single record from my table in Entity Framework 4?
I've primarily used SQL like SELECT * FROM {0} WHERE Id = {1}. That doesn't work in EF4, as far as I'm concerned.
Is there a way I can select a single ID-Based record from my Context?
Something like:
public Address GetAddress(int addressId)
{
var result = from Context.Addresses where Address.Id = addressId;
Address adr = result as Address;
return Address;
}
Thank you!
var address = Context.Addresses.First(a => a.Id == addressId);
You can use Single or First methods.
The difference between those methods is that Single expects a single row and throws an exception if it doesn't have a single row.
The usage is the same for both of them
(Based on VS 2015) If you create an .edmx (Add --> ADO.NET Entity Data Model).
Go through the steps to created the ".edmx" and use the following to run the stored procedure. emailAddress is the parameter you are passing to the stored procedure g_getLoginStatus. This will pull the first row into LoginStatus and status is a column in the database:
bool verasity = false;
DBNameEntities db = new DBNameEntities(); // Use name of your DBEntities
var LoginStatus = db.g_getLoginStatus(emailAddress).FirstOrDefault();
if ((LoginStatus != null) && (LoginStatus.status == 1))
{
verasity = true;
}