When I run this code:
korlenEntities2 _db = new korlenEntities2();
for (int i = 0; i < 10; i++)
{
klienci klient = new klienci();
klient.nazwa = "Janek_" + i.ToString();
klient.miejscowosc = "-";
_db.AddToklienci(klient);
};
_db.SaveChanges();
records are added to database in random order, so my field ID is not filled correctly. this is important to me since I want to use it for later ordering
You cannot control the order of query execution unless you call SaveChanges after every query. Nor can you depend on auto-incremented keys to be sequential in all cases (consider replication). If order is important, you should add a field for that.
Related
Need to sort/order a list of data based on an undetermined number of columns (1 or more).
What i'm trying to do is loop through the desired columns and add an OrderBy or ThenBy based on their number to the query'd list, but i'm unsuccessful...
Done this, but it doesn't compile:
var query = GetAllItems(); //returns a IQueriable list of items
//for each selected column
for (int i = 0; i < param.Columns.Length; i++)
{
if (i == 0)
{
query = query.OrderBy(x => x.GetType().GetProperty(param.Columns[i].Name));
}
else
{
//ERROR: IQueriable does not contain a definition for "ThenBy" and no extension method "ThenBy"...
query = query.ThenBy(x => x.GetType().GetProperty(param.Columns[i].Data));
}
}
How can i resolve this issue? Or any alternative to accomplish this requirement?
SOLUTION: #Dave-Kidder's solution is well thought and resolves the compile errors i had. Just one problem, OrderBy only executes (actually sorts the results) after a ToList() cast. This is an issue because i can't convert a ToList back to an IOrderedQueryable.
So, after some research i came across a solution that resolve all my issues.
Microsoft assembly for the .Net 4.0 Dynamic language functionality: https://github.com/kahanu/System.Linq.Dynamic
using System.Linq.Dynamic; //need to install this package
Updated Code:
var query = GetAllItems(); //returns a IQueriable list of items
List<string> orderByColumnList = new List<string>(); //list of columns to sort
for (int i = 0; i < param.Columns.Length; i++)
{
string column = param.Columns[i].Name;
string direction = param.Columns[i].Dir;
//ex.: "columnA ASC"
string orderByColumn = column + " " + direction;
//add column to list
orderByColumnList.Add(orderBy);
}
//convert list to comma delimited string
string orderBy = String.Join(",", orderByColumnList.ToArray());
//sort by all columns, yay! :-D
query.OrderBy(orderBy).ToList();
The problem is that ThenBy is not defined on IQueryable, but on the IOrderedQueryable interface (which is what IQueryable.OrderBy returns). So you need to define a new variable for the IOrderedQueryable in order to do subsequent ThenBy calls. I changed the original code a bit to use System.Data.DataTable (to get a similar structure to your "param" object). The code also assumes that there is at least one column in the DataTable.
// using System.Data.DataTable to provide similar object structure as OP
DataTable param = new DataTable();
IQueryable<DataTable> query = new List<DataTable>().AsQueryable();
// OrderBy returns IOrderedQueryable<TSource>, which is the interface that defines
// "ThenBy" so we need to assign it to a different variable if we wish to make subsequent
// calls to ThenBy
var orderedQuery = query.OrderBy(x => x.GetType().GetProperty(param.Columns[0].ColumnName));
//for each other selected column
for (int i = 1; i < param.Columns.Count; i++)
{
orderedQuery = orderedQuery.ThenBy(x => x.GetType().GetProperty(param.Columns[i].ColumnName));
}
you should write ThenBy after OrderBy like this:
query = query
.OrderBy(t=> // your condition)
.ThenBy(t=> // next condition);
A newbie question. I am using EntityFramework 4.0. The backend database has a function that will return a subset of records based on time.
Example of working code is:
var query = from rx in context.GetRxByDate(tencounter,groupid)
select rx;
var result = context.CreateDetachedCopy(query.ToList());
return result;
I need to verify that a record does not exist in the database before inserting a new record. Before performing the "Any" filter, I would like to populate the context.Rxes with a subset of the larger backend database using the above "GetRxByDate()" function.
I do not know how to populate "Rxes" before performing any further filtering since Rxes is defined as
IQueryable<Rx> Rxes
and does not allow "Rxes =.. ". Here is what I have so far:
using (var context = new EnityFramework())
{
if (!context.Rxes.Any(c => c.Cform == rx.Cform ))
{
// Insert new record
Rx r = new Rx();
r.Trx = realtime;
context.Add(r);
context.SaveChanges();
}
}
I am fully prepared to kick myself since I am sure the answer is simple.
All help is appreciated. Thanks.
Edit:
If I do it this way, "Any" seems to return the opposite results of what is expected:
var g = context.GetRxByDate(tencounter, groupid).ToList();
if( g.Any(c => c.Cform == rx.Cform ) {....}
I am using Entity Framework and my table structure is as below.
Key, dec2000, dec2001, dec2002,... dec2020
so, while update in loop if for all columns in i have to specify the column name like,
for (int j = 0; j < intEndYear - intStartYear; j++)
{
// Find value from FormCollection
// Assign it to object
OBJECT.DEC2000 = 1;
}
so, one way is i have to check for year and make condition check whether year = 2000 then use dec2000 field and so on.
So i tried to use Dynamic type so i can specify field name dynamically like
dynamic objLevel = objDetailSum.GetSingle(parameters);
so, while updating i am trying to do like
// trying to make field name
string stryear = "DEC" + year.ToString();
objLevel.stryear = 1; // should read objLevel.dec2000 = 1;
I know this will not work as i don't have strYear column in my table.
Question : Is there any other good way to handle this situation? so i don't have to check for each and every column and can use dynamic instead/.
Appreciate any direction.
You could use Reflection. See here for more information
//assuming "myInstance" is an instance of the EF class:
string strYear = "DEC"+year.ToString();
var pi =myInstance.GetType().GetProperty(styYear);
if (pi!=null)
{
pi.SetValue(MyInstance,1);
}
I'm new to BIRT and need an answer to the following question:
How to compare two data rows in one data set in BIRT and then print it out to the document?
I am assuming you have a reason for not using a self-join query to bring in the data. One simple thing you could do is have 2 identical datasets and then create a new joint dataset using the 2.
With an Oracle DB, you could easily achieve this with pure SQL using the "Analytic Function" LAG (see the Oracle documentation for details).
Independent from the DB, with BIRT, you could use a variable last_row:
Create some computed columns to keep the results of your comparisons. e.g. "FIRST_COLUMN_CHANGED" as boolean.
afterOpen event:
last_row = null;
onFetch event (pls note I'm not sure wether the actual data columns start at 0 or 1):
if (last_row != null) {
if (last_row[0] == row[0]) {
row["FIRST_COLUMN_CHANGED"] = false;
} else {
row["FIRST_COLUMN_CHANGED"] = true;
}
} else {
// do computations for the first record.
row["FIRST_COLUMN_CHANGED"] = true;
}
// Copy the current row to last_row
last_row = {};
// modify depending on the number of columns
for (var i=0; i<10; i++) {
last_row[i] = row[i];
}
I want to know why Code fragment 1 is faster than Code 2 using POCO's with Devart DotConnect for Oracle.
I tried it over 100000 records and Code 1 is way faster than 2. Why? I thought "SaveChanges" would clear the buffer making it faster as there is only 1 connection. Am I wrong?
Code 1:
for (var i = 0; i < 100000; i++)
{
using (var ctx = new MyDbContext())
{
MyObj obj = new MyObj();
obj.Id = i;
obj.Name = "Foo " + i;
ctx.MyObjects.Add(obj);
ctx.SaveChanges();
}
}
Code 2:
using (var ctx = new MyDbContext())
{
for (var i = 0; i < 100000; i++)
{
MyObj obj = new MyObj();
obj.Id = i;
obj.Name = "Foo " + i;
ctx.MyObjects.Add(obj);
ctx.SaveChanges();
}
}
The first code snippet works faster as the same connection is taken from the pool every time, so there are no performance losses on its re-opening.
In the second case 100000 objects gradually are added to the context. A slow snapshot-based tracking is used (if no dynamic proxy). This leads to the detection if any changes in any of cached objects occured on each SaveChanges(). More and more time is spent by each subsequent iteration.
We recommend you to try the following approach. It should have a better performance than the mentioned ones:
using (var ctx = new MyDbContext())
{
for (var i = 0; i < 100000; i++)
{
MyObj obj = new MyObj();
obj.Id = i;
obj.Name = "Foo " + i;
ctx.MyObjects.Add(obj);
}
ctx.SaveChanges();
}
EDIT
If you use an approach with executing large number of operations within one SaveChanges(), it will be useful to configure additionally the Entity Framework behaviour of Devart dotConnect for Oracle provider:
// Turn on the Batch Updates mode:
var config = OracleEntityProviderConfig.Instance;
config.DmlOptions.BatchUpdates.Enabled = true;
// If necessary, enable the mode of re-using parameters with the same values:
config.DmlOptions.ReuseParameters = true;
// If object has a lot of nullable properties, and significant part of them are not set (i.e., nulls), omitting explicit insert of NULL-values will decrease greatly the size of generated SQL:
config.DmlOptions.InsertNullBehaviour = InsertNullBehaviour.Omit;
Only some options are mentioned here. The full list of them is available in our article:
http://www.devart.com/blogs/dotconnect/index.php/new-features-of-entity-framework-support-in-dotconnect-providers.html
Am I wrong to assume that when SaveChanges() is called, all the
objects in cache are stored to DB and the cache is cleared, so each
loop is independent?
SaveChanges() sends and commits all changes to database, but change tracking is continued for all entities which are attached to the context. And new SaveChanges, if snapshot-based change tracking is used, will start a long process of checking (changed or not?) the values of each property for each object.