Dynamically update table using Dynamic LINQ - entity-framework-6

I have a list of column names and I want to dynamically update table and set all the rows for those columns to NULL. The current code is using if logic and it need to keep updating when list of columns changes
var columns = new string[] {"FirstName","LastName"};
using(var scope = new TransactionScope())
{
foreach(var col in columns)
{
if(col == "FirstName")
{
dbContext.Users
.Where(x=>x.ParentID = 1234)
.Update(x=> new User()
{
FirstName = null
}
}
if(col == "LastName")
{
dbContext.Users
.Where(x=>x.ParentID = 1234)
.Update(x=> new User()
{
LastName = null
}
}
}
scope.Complete();
}
I am also using Dynamic LINQ and Z Framework with EF 6. Is there a way to update table certain columns dynamically?
(I can also construct sql update string execute as CommandText but I am trying to avoid that)

Disclaimer: I'm the owner of the project Entity Framework Plus
The UpdateFromQuery similar to Update from EF Extensions allow to uses ExpandoObject and IDictionary<string, object>
For example:
Dictionary<string, object> dict = new Dictionary<string, object>();
dict.Add("FirstName", null);
dbContext.Users
.Where(x=>x.ParentID = 1234)
.UpdateFromQuery(dict);
Next week, the Update method will also support it, I will update my answer at this time.
UPDATED
Since the v5.1.29, the Update method also support dictionary
Dictionary<string, object> dict = new Dictionary<string, object>();
dict.Add("FirstName", null);
dbContext.Users
.Where(x=>x.ParentID = 1234)
.Update(dict);

Related

Best Way to Update only modified fields with Entity Framework

Currently I am doing like this:
For Example:
public update(Person model)
{
// Here model is model return from form on post
var oldobj = db.Person.where(x=>x.ID = model.ID).SingleOrDefault();
db.Entry(oldobj).CurrentValues.SetValues(model);
}
It works, but for example,
I have 50 columns in my table but I displayed only 25 fields in my form (I need to partially update my table, with remaining 25 column retain same old value)
I know it can be achieve by "mapping columns one by one" or by creating "hidden fields for those remaining 25 columns".
Just wondering is there any elegant way to do this with less effort and optimal performance?
This is a very good question. By default I have found that as long as change tracking is enabled (it is by default unless you turn it off), Entity Framework will do a good job of applying to the database only what you ask it to change.
So if you only change 1 field against the object and then call SaveChanges(), EF will only update that 1 field when you call SaveChanges().
The problem here is that when you map a view model into an entity object, all of the values get overwritten. Here is my way of handling this:
In this example, you have a single entity called Person:
Person
======
Id - int
FirstName - varchar
Surname - varchar
Dob - smalldatetime
Now let's say we want to create a view model which will only update Dob, and leave all other fields exactly how they are, here is how I do that.
First, create a view model:
public class PersonDobVm
{
public int Id { get; set; }
public DateTime Dob { get; set; }
public void MapToModel(Person p)
{
p.Dob = Dob;
}
}
Now write the code roughly as follows (you'll have to alter it to match your context name etc):
DataContext db = new DataContext();
Person p = db.People.FirstOrDefault();
// you would have this posted in, but we are creating it here just for illustration
var vm = new PersonDobVm
{
Id = p.Id, // the Id you want to update
Dob = new DateTime(2015, 1, 1) // the new DOB for that row
};
vm.MapToModel(p);
db.SaveChanges();
The MapToModel method could be even more complicated and do all kinds of additional checks before assigning the view model fields to the entity object.
Anyway, the result when SaveChanges is called is the following SQL:
exec sp_executesql N'UPDATE [dbo].[Person]
SET [Dob] = #0
WHERE ([Id] = #1)
',N'#0 datetime2(7),#1 int',#0='2015-01-01 00:00:00',#1=1
So you can clearly see, Entity Framework has not attempted to update any other fields - just the Dob field.
I know in your example you want to avoid coding each assignment by hand, but I think this is the best way. You tuck it all away in your VM so it does not litter your main code, and this way you can cater for specific needs (i.e. composite types in there, data validation, etc). The other option is to use an AutoMapper, but I do not think they are safe. If you use an AutoMapper and spelt "Dob" as "Doob" in your VM, it would not map "Doob" to "Dob", nor would it tell you about it! It would fail silently, the user would think everything was ok, but the change would not be saved.
Whereas if you spelt "Dob" as "Doob" in your VM, the compiler will alert you that the MapToModel() is referencing "Dob" but you only have a property in your VM called "Doob".
I hope this helps you.
I swear by EntityFramework.Extended. Nuget Link
It lets you write:
db.Person
.Where(x => x.ID == model.ID)
.Update(p => new Person()
{
Name = newName,
EditCount = p.EditCount+1
});
Which is very clearly translated into SQL.
Please 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();
// Newly Inserted Code
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;
}
I have solved my Issue by using FormCollection to list out used element in form, and only change those columns in database.
I have provided my code sample below; Great if it can help someone else
// Here
// collection = FormCollection from Post
// model = View Model for Person
var result = db.Person.Where(x => x.ID == model.ID).SingleOrDefault();
if (result != null)
{
List<string> formcollist = new List<string>();
foreach (var key in collection.ToArray<string>())
{
// Here apply your filter code to remove system properties if any
formcollist.Add(key);
}
foreach (var prop in result.GetType().GetProperties())
{
if( formcollist.Contains(prop.Name))
{
prop.SetValue(result, model.GetType().GetProperty(prop.Name).GetValue(model, null));
}
}
db.SaveChanges();
}
I still didn't find a nice solution for my problem, so I created a work around. When loading the Entity, I directly make a copy of it and name it entityInit. When saving the Entity, I compare the both to see, what really was changed. All the unchanged Properties, I set to unchanged and fill them with the Database-Values. This was necessary for my Entities without Tracking:
// load entity without tracking
var entityWithoutTracking = Context.Person.AsNoTracking().FirstOrDefault(x => x.ID == _entity.ID);
var entityInit = CopyEntity(entityWithoutTracking);
// do business logic and change entity
entityWithoutTracking.surname = newValue;
// for saving, find entity in context
var entity = Context.Person.FirstOrDefault(x => x.ID == _entity.ID);
var entry = Context.Entry(entity);
entry.CurrentValues.SetValues(entityWithoutTracking);
entry.State = EntityState.Modified;
// get List of all changed properties (in my case these are all existing properties, including those which shouldn't have changed)
var changedPropertiesList = entry.CurrentValues.PropertyNames.Where(x => entry.Property(x).IsModified).ToList();
foreach (var checkProperty in changedPropertiesList)
{
try
{
var p1 = entityWithoutTracking.GetType().GetProperty(checkProperty).GetValue(entityWithoutTracking);
var p2 = entityInit.GetType().GetProperty(checkProperty).GetValue(entityInit);
if ((p1 == null && p2 == null) || p1.Equals(p2))
{
entry.Property(checkProperty).CurrentValue = entry.Property(checkProperty).OriginalValue; // restore DB-Value
entry.Property(checkProperty).IsModified = false; // throws Exception for Primary Keys
}
} catch(Exception) { }
}
Context.SaveChanges(); // only surname will be updated
This is way I did it, assuming the new object has more columns to update that the one we want to keep.
if (theClass.ClassId == 0)
{
theClass.CreatedOn = DateTime.Now;
context.theClasses.Add(theClass);
}
else {
var currentClass = context.theClasses.Where(c => c.ClassId == theClass.ClassId)
.Select(c => new TheClasses {
CreatedOn = c.CreatedOn
// Add here others fields you want to keep as the original record
}).FirstOrDefault();
theClass.CreatedOn = currentClass.CreatedOn;
// The new class will replace the current, all fields
context.theClasses.Add(theClass);
context.Entry(theClass).State = EntityState.Modified;
}
context.SaveChanges();
In EF you can do like this
var result = db.Person.Where(x => x.ID == model.ID).FirstOrDefault();
if(result != null){
result.Name = newName;
result.DOB = newDOB;
db.Person.Update(result);
}
Or you can use
using (var db= new MyDbContext())
{
var result= db.Person.Where(x => x.ID == model.ID).FirstOrDefault();
result.Name= newName;
result.DOB = newDOB;
db.Update(result);
db.SaveChanges();
}
For more detail please EntityFramework Core - Update Only One Field
No Worry guys
Just write raw sql query
db.Database.ExecuteSqlCommand("Update Person set Name='"+_entity.Name+"' where Id = " + _entity.ID + "");

How to get all values in a column in table using vaadin SQLContainer

Hi Stackoverflow members,
I have one SQLContainer with TableQuery. Now, I want to get all the values in one column. How can I get it? Or Shall I need to go with FreefromQuery?
This is my SQLContainer code
public SQLContainer getMyContainer() {
//FreeformQuery query = null;
SQLContainer container = null;
try {
connectionPool = new SimpleJDBCConnectionPool(
"com.mysql.jdbc.Driver",
"jdbc:mysql://localhost:3306/vaadin", "root", "root",
2, 5);
TableQuery query = new TableQuery("components", connectionPool);
/*query = new FreeformQuery(
"SELECT rowNum, colNum, caption, cType FROM items where screenId='"
+ screenName+"'", connectionPool);
query.setDelegate(new DemoFreeformQueryDelegate());*/
container = new SQLContainer(query);
} catch (Exception e) {
}
return container;
}
It depends on what you wish to do.
With SQLContainer you could do it this way:
// Returns a list with all ID's (Beware of large resultsets)
Collection<?> itemIDS= conatiner.getItemIds();
for (Object itemID : itemIDS)
{
Property property= container.getContainerProperty(itemID, "COLUMN");
Object data= property.getValue();
}
The getItemIds() must fetch all rows from the DB (at least the primary keys),
so this will cause troubles with large resultsets/tables.
https://vaadin.com/api/com/vaadin/data/util/sqlcontainer/SQLContainer.html#getItemIds%28%29

LINQ to Entities StringConvert(double)' cannot be translated to convert int to string

Problem
Need to convert int to string using EF4 + SQL CE4. The recommended option of using SqlFunctions.StringConvert(double) still gives me errors.
Option 1 (original). This gives me error:
public static IEnumerable<SelectListItem> xxGetCustomerList()
{
using (DatabaseEntities db = new DatabaseEntities())
{
var list = from l in db.Customers
orderby l.CompanyName
select new SelectListItem { Value = l.CustomerID.ToString(), Text = l.CompanyName };
return list.ToList();
}
}
Option 2 (most suggested). Then as many posts suggests, I used the SqlFunctions.StringConvert() function from the library System.Data.Objects.SqlClient:
public static IEnumerable<SelectListItem> GetCustomerList()
{
using (DatabaseEntities db = new DatabaseEntities())
{
var list = from l in db.Customers
orderby l.CompanyName
select new SelectListItem { Value = SqlFunctions.StringConvert((double)l.CustomerID), Text = l.CompanyName };
return list.ToList();
}
}
Which now shows below error:
The specified method 'System.String StringConvert(System.Nullable`1[System.Double])' on the type 'System.Data.Objects.SqlClient.SqlFunctions' cannot be translated into a LINQ to Entities store expression.
Option 3 (for very specific case). Then anoter post shows a smart solution using Dictionary, which finally works:
public static IEnumerable<SelectListItem> xGetCustomerList()
{
using (DatabaseEntities db = new DatabaseEntities())
{
var customers = db.Customers.ToDictionary(k => k.CustomerID, k => k.CompanyName);
var list = from l in customers
orderby l.Value
select new SelectListItem { Value = l.Key.ToString(), Text = l.Value };
return list.ToList();
}
}
But only work for simple pair values (key, value). Can someone help me with another solution or what I'm doing wrong with option 2?
And I hope Microsoft will soon make EF right before pushing us to move from L2S which is already stable and much more mature. I actually using EF4 just because want to use SQL CE, otherwise I stay with L2S.
EF is database independent at upper layers but the part dealing with conversion of linq query to SQL is always database dependent and SqlFunctions are dependent on SQL Server Provider but you are using SQL Server CE provider which is not able to translate functions from SqlFunctions class.
Btw. third option is also not a solution because it will select whole customer table to memory and use linq-to-objects after that. You should use this:
public static IEnumerable<SelectListItem> xxGetCustomerList()
{
using (DatabaseEntities db = new DatabaseEntities())
{
// Linq to entities query
var query = from l in db.Customers
orderby l.CompanyName
select new { l.CustomerID, l.CompanyName };
// Result of linq to entities transformed by linq to objects
return query.AsEnumerable()
.Select(x => new SelectListItem
{
Value = x.CustomerID.ToString(),
Test = x.CompanyName
}).ToList();
}
}
Here is a simplified version I'm using now (specific for SQL CE):
public static IEnumerable<SelectListItem> GetBlogCategoryList()
{
using (SiteDataContext db = new SiteDataContext())
{
var list = from l in db.BlogCategories.AsEnumerable()
orderby l.CategoryName
select new SelectListItem { Value = l.CategoryID.ToString(), Text = l.CategoryName };
return list.ToList();
}
}
Note the db.BlogCategories.AsEnumerable() part

Asp.Net MVC 3 - Linq To Entities - PK with Null doesn't get inserted into the db (don't want null :))

I'm using the latest Asp.Net MVC version.
For some reason, when my POST (Action Create) in my controller gets hit.
I can't seem to be able to add it to the entityset.
What i have is,
1) My EntityModel (*.edmx file)
2) Controller which references the entity:
private db.DataContainer _db = new db.DataContainer();
3) My method (i'm using Guid as pk):
[HttpPost]
public ActionResult Create(Client client)
{
try
{
client.Id = Guid.NewGuid();
/* method 2
Client cl = new Client();
cl.Id = Guid.NewGuid();
cl.email = client.email;
cl.Adres = client.Adres;
cl.companyName = client.companyName;
cl.fax = client.fax;
cl.phone = client.phone;
*/
// client.Id = Guid.NewGuid();
_db.ClientSet.AddObject(client);
_db.SaveChanges();
return RedirectToAction("Index");
}
catch (Exception ex)
{
var ex_message = ex.Message;
var ex_data = ex.Data;
var ex_ix = ex.InnerException;
return View();
}
}
4) Following is my InnerException:
[System.Data.SqlClient.SqlException] = {"Cannot insert the value NULL into column 'Id', table 'lst.dbo.ClientSet'; column does not allow nulls. INSERT fails.\r\nThe statement has been terminated."}
Both doesn't seem to work :(
GUIDs are not supported as primary keys in the Entity Framework. You will need to modify your save method to generate a new GUID for your added objects http://msdn.microsoft.com/en-us/library/dd283139.aspx
It seems that changing my "saveCommand" has given my a temporarily solution:
I chaned:
_db.SaveChanges()
To
_db.SaveChanges(System.Data.Objects.SaveOptions.None);

How do you persist changes to objects returned from a LINQ query to the database?

So I load up an object like...
MyObject object = new MyObject();
object = objectRepository.getObjectByID(id);
object.lastLoaded = DateTime.Now();
...
//NOW WHAT????
I know there is a .Save() but does that update the current one or is that only used for creating new ones?
You want to use the SubmitChanges() method available on your DataContext.
Quick example:
public void updateLoadDate(int id)
{
using(LinqDataContext db = new LinqDataContext())
{
var myObject = (from object in db.objects
where object.id == id
select object).SingleOrDefault();
myObject.lastloaded = DateTime.Now();
db.SubmitChanges();
}
}

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