i just use userIdx of findAllregions's parameter to findFavoriteStore
this is my query
#Select("SELECT * FROM region")
#Results(value = {
#Result(property = "regionIdx", column = "regionIdx"),
#Result(property = "stores", javaType = Store.class, column = "storeIdx",
many = #Many(select = "com.travely.travely.mapper.StoreMapper.findFavoriteStore", fetchType = FetchType.LAZY))
})
List<Region> findAllRegions(#Param("userIdx") final Long useridx);
#Select("SELECT s.* FROM store as s NATURAL JOIN favorite as f WHERE f.userIdx=#{userIdx} AND f.isFavorite = 1")
List<Store> findFavoriteStore(#Param("userIdx") final long userIdx);
it works to select region of 'findAllRegions'
but doesn't work to select store of 'findFavoriteStore'
The query does not work because the column attribute is configured incorrectly.
Here is relevant part of the column attribute documentation:
The column name from the database, or the aliased column label that
holds the value that will be passed to the nested statement as an
input parameter.
As you see only the column from the main query result can be used.
It means that you either need to include the artificial column to the query and use it in the #Result.column like this:
#Select("SELECT #{userIdx} userIdx, r.* FROM region r")
#Results(value = {
#Result(property = "regionIdx", column = "regionIdx"),
#Result(
property = "stores", javaType = Store.class, column = "userIdx",
many = #Many(
select = "com.travely.travely.mapper.StoreMapper.findFavoriteStore",
fetchType = FetchType.LAZY))
})
List<Region> findAllRegions(#Param("userIdx") final Long useridx);
Alternatively if java 8+ is used you can use default interface methods to fetch associations/collections like this:
interfact MyMapper {
#Select("SELECT * FROM region")
#Results(value = {
#Result(property = "regionIdx", column = "regionIdx")
})
List<Region> findAllRegions();
default List<Region> findAllRegions(Long userIdx) {
List<Region> regions = findAllRegions();
List<Strore> favoriteStores = findFavoriteStore(userIdx);
for(Region region:regions) {
region.setStores(favoriteStores);
}
return regions;
}
#Select("SELECT s.* FROM store as s NATURAL JOIN favorite as f WHERE f.userIdx=#{userIdx} AND f.isFavorite = 1")
List<Store> findFavoriteStore(#Param("userIdx") final long userIdx);
}
Note that this does not use lazy fetching of the favourite stores. It seems that this is not needed as in the contexts that favorite stores are not needed the query without userIdx can (and should0 be used.
Related
As stated in official documentation, it's preferable to use the Multimap return type for the Android Room database.
With the next very simple example, it's not working correctly!
#Entity
data class User(#PrimaryKey(autoGenerate = true) val _id: Long = 0, val name: String)
#Entity
data class Book(#PrimaryKey(autoGenerate = true) val _id: Long = 0, val bookName: String, val userId: Long)
(I believe a loooot of the developers have the _id primary key in their tables)
Now, in the Dao class:
#Query(
"SELECT * FROM user " +
"JOIN book ON user._id = book.userId"
)
fun allUserBooks(): Flow<Map<User, List<Book>>>
The database tables:
Finally, when I run the above query, here is what I get:
While it should have 2 entries, as there are 2 users in the corresponding table.
PS. I'm using the latest Room version at this point, Version 2.4.0-beta02.
PPS. The issue is in how UserDao_Impl.java is being generated:
all the _id columns have the same index there.
Is there a chance to do something here? (instead of switching to the intermediate data classes).
all the _id columns have the same index there.
Is there a chance to do something here?
Yes, use unique column names e.g.
#Entity
data class User(#PrimaryKey(autoGenerate = true) val userid: Long = 0, val name: String)
#Entity
data class Book(#PrimaryKey(autoGenerate = true) valbookid: Long = 0, val bookName: String, val useridmap: Long)
as used in the example below.
or
#Entity
data class User(#PrimaryKey(autoGenerate = true) #ColumnInfo(name="userid")val _id: Long = 0, val name: String)
#Entity
data class Book(#PrimaryKey(autoGenerate = true) #ColumnInfo(name="bookid")val _id: Long = 0, val bookName: String, val #ColumnInfo(name="userid_map")userId: Long)
Otherwise, as you may have noticed, Room uses the value of the last found column with the duplicated name and the User's _id is the value of the Book's _id column.
Using the above and replicating your data using :-
db = TheDatabase.getInstance(this)
dao = db.getAllDao()
var currentUserId = dao.insert(User(name = "Eugene"))
dao.insert(Book(bookName = "Eugene's book #1", useridmap = currentUserId))
dao.insert(Book(bookName = "Eugene's book #2", useridmap = currentUserId))
dao.insert(Book(bookName = "Eugene's book #3", useridmap = currentUserId))
currentUserId = dao.insert(User(name = "notEugene"))
dao.insert(Book(bookName = "not Eugene's book #4", useridmap = currentUserId))
dao.insert(Book(bookName = "not Eugene's book #5", useridmap = currentUserId))
var mapping = dao.allUserBooks() //<<<<<<<<<< BREAKPOINT HERE
for(m: Map.Entry<User,List<Book>> in mapping) {
}
for convenience and brevity a Flow hasn't been used and the above was run on the main thread.
Then the result is what I believe you are expecting :-
Additional
What if we already have the database structure with a lot of "_id" fields?
Then you have some decisions to make.
You could
do a migration to rename columns to avoid the ambiguous/duplicate column names.
use alternative POJO's in conjunction with changing the extract output column names accordingly
e.g. have :-
data class Alt_User(val userId: Long, val name: String)
and
data class Alt_Book (val bookId: Long, val bookName: String, val user_id: Long)
along with :-
#Query("SELECT user._id AS userId, user.name, book._id AS bookId, bookName, user_id " +
"FROM user JOIN book ON user._id = book.user_id")
fun allUserBooksAlt(): Map<Alt_User, List<Alt_Book>>
so user._id is output with the name as per the Alt_User POJO
other columns output specifically (although you could use * as per allUserBookAlt2)
:-
#Query("SELECT *, user._id AS userId, book._id AS bookId " +
"FROM user JOIN book ON user._id = book.user_id")
fun allUserBooksAlt2(): Map<Alt_User, List<Alt_Book>>
same as allUserBooksAlt but also has the extra columns
you would get a warning warning: The query returns some columns [_id, _id] which are not used by any of [a.a.so70190116kotlinroomambiguouscolumnsfromdocs.Alt_User, a.a.so70190116kotlinroomambiguouscolumnsfromdocs.Alt_Book]. You can use #ColumnInfo annotation on the fields to specify the mapping. You can annotate the method with #RewriteQueriesToDropUnusedColumns to direct Room to rewrite your query to avoid fetching unused columns. You can suppress this warning by annotating the method with #SuppressWarnings(RoomWarnings.CURSOR_MISMATCH). Columns returned by the query: _id, name, _id, bookName, user_id, userId, bookId. public abstract java.util.Map<a.a.so70190116kotlinroomambiguouscolumnsfromdocs.Alt_User, java.util.List<a.a.so70190116kotlinroomambiguouscolumnsfromdocs.Alt_Book>> allUserBooksAlt2();
Due to Note that Room will not rewrite the query if it has multiple columns that have the same name as it does not yet have a way to distinguish which one is necessary. the #RewriteQueriesToDropUnusedColumns doesn't do away with the warning.
if using :-
var mapping = dao.allUserBooksAlt() //<<<<<<<<<< BREAKPOINT HERE
for(m: Map.Entry<Alt_User,List<Alt_Book>> in mapping) {
}
Would result in :-
possibly other options.
However, I'd suggest fixing the issue once and for all by using a migration to rename columns to all have unique names. e.g.
I have a table form_header with 3 records
There are more fields in the table decided not to add it here in the post since most are irrelevant. I created a class/entity to get the count with distinct for each status in sql.
#Entity()
#Table(name = "Form_Header")
#SqlResultSetMapping(name = "myMapping",
entities = {#EntityResult(
entityClass = FormSummary.class,
fields = {#FieldResult(name = "status", column = "status"),
#FieldResult(name = "id", column = "header_id")})})
public class FormSummary {
#Id()
private Long id;
private String status;
<getter and setter>
with entity manager
List<FormSummary> results = entityManager.createNativeQuery("select DISTINCT(status), COUNT(header_id) as header_id from Form_Header where is_deleted = 0 group by status order by status", "myMapping").getResultList();
for (FormSummary x : results) {
System.out.println("ABC " + x.getId());
System.out.println("ABC " + x.getStatus());
}
Issue is the sysout is showing this
instead of this
status header_id
APPROVE 1
DRAFT 1
SUBMITTED 1
Whats even weird is if I add an extra record in the table with the same status
I will get the correct data in my jpa
Am I missing something in my code or a possible bug with SqlResultSetMapping?
Using Linq commands and Linq To SQL datacontext, Im trying to instance an Entity called "Produccion" from my datacontext in this way:
Demo.View.Data.PRODUCCION pocoProduccion =
(
from m in db.MEDICOXPROMOTORs
join a in db.ATENCIONs on m.cmp equals a.cmp
join e in db.EXAMENXATENCIONs on a.numeroatencion equals e.numeroatencion
join c in db.CITAs on e.numerocita equals c.numerocita
where e.codigo == codigoExamenxAtencion
select new Demo.View.Data.PRODUCCION
{
cmp = a.cmp,
bonificacion = comi,
valorventa = precioEstudio,
codigoestudio = lblCodigoEstudio.Content.ToString(),
codigopaciente = Convert.ToInt32(lblCodigoPaciente.Content.ToString()),
codigoproduccion = Convert.ToInt32(lblNroInforme.Content.ToString()),
codigopromotor = m.codigopromotor,
fecha = Convert.ToDateTime(DateTime.Today.ToShortDateString()),
numeroinforme = Convert.ToInt32(lblNroInforme.Content.ToString()),
revisado = false,
codigozona = (c.codigozona.Value == null ? Convert.ToInt32(c.codigozona) : 0),
codigoclinica = Convert.ToInt32(c.codigoclinica),
codigoclase = e.codigoclase,
}
).FirstOrDefault();
While executing the above code, I'm getting the following error that the stack trace is included:
System.NotSupportedException was caught
Message="The explicit construction of the entity type 'Demo.View.Data.PRODUCCION' in a query is not allowed."
Source="System.Data.Linq"
StackTrace:
en System.Data.Linq.SqlClient.QueryConverter.VisitMemberInit(MemberInitExpression init)
en System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.VisitSelect(Expression sequence, LambdaExpression selector)
en System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.VisitFirst(Expression sequence, LambdaExpression lambda, Boolean isFirst)
en System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.ConvertOuter(Expression node)
en System.Data.Linq.SqlClient.SqlProvider.BuildQuery(Expression query, SqlNodeAnnotations annotations)
en System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
en System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute[S](Expression expression)
en System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
en Demo.View.InformeMedico.realizarProduccionInforme(Int32 codigoExamenxAtencion, Double precioEstudio, Int32 comi) en D:\cs_InformeMedico\app\InformeMedico.xaml.cs:línea 602
en Demo.View.InformeMedico.UpdateEstadoEstudio(Int32 codigo, Char state) en D:\cs_InformeMedico\app\InformeMedico.xaml.cs:línea 591
en Demo.View.InformeMedico.btnGuardar_Click(Object sender, RoutedEventArgs e) en D:\cs_InformeMedico\app\InformeMedico.xaml.cs:línea 683
InnerException:
Is that now allowed in LINQ2SQL?
Entities can be created outside of queries and inserted into the data store using a DataContext. You can then retrieve them using queries. However, you can't create entities as part of a query.
I am finding this limitation to be very annoying, and going against the common trend of not using SELECT * in queries.
Still with c# anonymous types there is a workaround, by fetching the objects into an anonymous type, and then copy it over into the correct type.
For example:
var q = from emp in employees where emp.ID !=0
select new {Name = emp.First + " " + emp.Last, EmployeeId = emp.ID }
var r = q.ToList();
List<User> users = new List<User>(r.Select(new User
{
Name = r.Name,
EmployeeId = r.EmployeeId
}));
And in the case when we deal with a single value (as in the situation described in the question) it is even easier, and we just need to copy directly the values:
var q = from emp in employees where emp.ID !=0
select new { Name = emp.First + " " + emp.Last, EmployeeId = emp.ID }
var r = q.FirstOrDefault();
User user = new User { Name = r.Name, EmployeeId = r.ID };
If the name of the properties match the database columns we can do it even simpler in the query, by doing select
var q = from emp in employees where emp.ID !=0
select new { emp.First, emp.Last, emp.ID }
One might go ahead and write a lambda expression that can copy automatically based on the property name, without needing to specify the values explictly.
Here's another workaround:
Make a class that derives from your LINQ to SQL class. I'm assuming that the L2S class that you want to return is Order:
internal class OrderView : Order { }
Now write the query this way:
var query = from o in db.Order
select new OrderView // instead of Order
{
OrderID = o.OrderID,
OrderDate = o.OrderDate,
// etc.
};
Cast the result back into Order, like this:
return query.Cast<Order>().ToList(); // or .FirstOrDefault()
(or use something more sensible, like BLToolkit / LINQ to DB)
Note: I haven't tested to see if tracking works or not; it works to retrieve data, which is what I needed.
I have found that if you do a .ToList() on the query before trying to contruct new objects it works
I just ran into the same issue.
I found a very easy solution.
var a = att as Attachment;
Func<Culture, AttachmentCulture> make =
c => new AttachmentCulture { Culture = c };
var culs = from c in dc.Cultures
let ac = c.AttachmentCultures.SingleOrDefault(
x => x.Attachment == a)
select ac == null ? make(c) : ac;
return culs;
I construct an anonymous type, use IEnumerable (which preserves deferred execution), and then re-consruct the datacontext object. Both Employee and Manager are datacontext objects:
var q = dc.Employees.Where(p => p.IsManager == 1)
.Select(p => new { Id = p.Id, Name = p.Name })
.AsEnumerable()
.Select(item => new Manager() { Id = item.Id, Name = item.Name });
Within the book "70-515 Web Applications Development with Microsoft .NET Framework 4 - Self paced training kit", page 638 has the following example to output results to a strongly typed object:
IEnumerable<User> users = from emp in employees where emp.ID !=0
select new User
{
Name = emp.First + " " + emp.Last,
EmployeeId = emp.ID
}
Mark Pecks advice appears to contradict this book - however, for me this example still displays the above error as well, leaving me somewhat confused. Is this linked to version differences? Any suggestions welcome.
I found another workaround for the problem that even lets you retain your result as IQueryale, so it doesn't actually execute the query until you want it to be executed (like it would with the ToList() method).
So linq doesn't allow you to create an entity as a part of query? You can shift that task to the database itself and create a function that will grab the data you want. After you import the function to your data context, you just need to set the result type to the one you want.
I found out about this when I had to write a piece of code that would produce a IQueryable<T> in which the items don't actually exist in the table containing T.
pbz posted a work around by creating a View class inherited from an entity class that you could be working with. I'm working with a dbml model of a table that has > 200 columns. When I try and return the whole table I get "Root Element missing" errors. I couldn't find anyone who wanted to deal with my particular issue so I was looking at rewriting my entire approach. Just creating a view class for the entitiy class worked in my case.
As pbz suggests : Create a view class that inherits from your entity class. For me this is tbCamp so :
internal class tbCampView : tbCamp
{
}
Then use the view class in your query :
using (var dc = ConnectionClass.Connect(Dev))
{
var camps = dc.tbCamps.Select(s => new tbCampView
{
active = s.active,
idCamp = s.idCamp,
campName = s.campName
});
SmartTableViewer(camps, dg1);
}
private void SmartTableViewer<T>(IEnumerable<T> allRecords)
{
// Build sorted rows back into new table
var table = new DataTable();
// Create columns based on type
if (allRecords is IEnumerable<tbCamp> tbCampRecords)
{
// Get the columns you want
table.Columns.Add("idCamp");
table.Columns.Add("campName");
foreach (var record in tbCampRecords)
{
// Make a new row
var r = table.NewRow();
// Add the contents to each column of the row
r["idCamp"] = record.idCamp;
r["campName"] = record.campName;
// Add the row to the table.
table.Rows.Add(r);
}
}
else
{
MessageBox.Show("Unhandled type. Add support for new data type in SmartTableViewer()");
return;
}
// Update table in grid
dg1.DataSource = table.DefaultView;
}
Here is what happens when you try and create an entity class object in the query.
I didn't want to have to use an anonymous type if I could help it because I wanted the type to be tbCamp. Since tbCampView is of type tbCamp the is operator works well. see Brian Hasden's answer Passing a generic List<> in C#
I'm surprised this is even an issue but with larger tables I run into this error so I thought I would just show it here :
When trying to read this table into memory I get the following error. There are < 2000 rows but the columns are > 200 for each. I don't know if that is an issue or not.
If I just want a few columns I need to create a custom class and handle that which isn't that big of a pain. With the approach pbz provided I don't have to worry about it.
Here is the entire project in case it helps someone.
public partial class Form1 : Form
{
private const bool Dev = true;
public Form1()
{
InitializeComponent();
}
private void btnGetAllCamps_Click(object sender, EventArgs e)
{
using (var dc = ConnectionClass.Connect(Dev))
{
IQueryable<tbCampView> camps = dc.tbCamps.Select(s => new tbCampView
{
// Project columns as needed.
active = s.active,
idCamp = s.idCamp,
campName = s.campName
});
// pass in as a
SmartTableViewer(camps);
}
}
private void SmartTableViewer<T>(IEnumerable<T> allRecords)
{
// Build sorted rows back into new table
var table = new DataTable();
// Create columns based on type
if (allRecords is IEnumerable<tbCamp> tbCampRecords)
{
// Get the columns you want
table.Columns.Add("idCamp");
table.Columns.Add("campName");
foreach (var record in tbCampRecords)
{
//var newRecord = record;
// Make a new row
var r = table.NewRow();
// Add the contents to each column of the row
r["idCamp"] = record.idCamp;
r["campName"] = record.campName;
// Add the row to the table.
table.Rows.Add(r);
}
}
else
{
MessageBox.Show("Unhandled type. Add support for new data type in SmartTableViewer()");
return;
}
// Update table in grid
dg1.DataSource = table.DefaultView;
}
internal class tbCampView : tbCamp
{
}
}
In my code I have the following Linq Query:
IQueryable<Data> charts = (from report in ctx.Charts group report by new
{
Name = report.ChartTitle.ChartType.ChartCategory.CategoryName,
id = report.ChartTitle.ChartType.ChartCategory.ChartCategoryId,
Period = report.Period
} into d
select new Data
{
Name = d.Key.Name,
Id = d.Key.id,
Period = d.Key.Period,
Reports = from r in d group r by new
{ Title = r.ChartTitle.Name, id = r.ChartTitle.ChartTitleId } into rs
select new Report
{
Title = rs.Key.Title,
Id = rs.Key.id,
Charts = (from c in rs group c by new
{
ChartId = c.ChartId,
FiscalYear = c.FiscalYear,
ModifiedDate = c.ChartView.ModifiedDate,
Function = c.Function.DisplayName,
ChartData=c.ChartView.ViewData
} into cs
select new ChartInfo
{
ChartId = cs.Key.ChartId,
FiscalYear = cs.Key.FiscalYear,
ModifiedDate = cs.Key.ModifiedDate,
Function = cs.Key.Function,
ChartData=cs.Key.ChartData
})
}});
In the above code if I exclude the "ChartData" field (which is of XML datatype), the query executes fine. But when ever I include this field it throws the following error :"The xml data type cannot be selected as DISTINCT because it is not comparable."
Let me know what I am missing here?
You can't group by XML types. This is a SQL restriction, not a LINQ-to-SQL retriction. (See Group by on XML column field with LINQ and select an xml type column in select query with group by SQL Server 2008)
Do you need to group by the XML column? The alternative would be to group by your other columns and then select the first XML value as a result.
Charts = (from c in rs group c by new
{
ChartId = c.ChartId,
FiscalYear = c.FiscalYear,
ModifiedDate = c.ChartView.ModifiedDate,
Function = c.Function.DisplayName,
} into cs
select new ChartInfo
{
ChartId = cs.Key.ChartId,
FiscalYear = cs.Key.FiscalYear,
ModifiedDate = cs.Key.ModifiedDate,
Function = cs.Key.Function,
ChartData=cs.Value.FirstOrDefault().ChartData
})
When using LINQ-to-SQL the items being grouped are still accessible - you don't need to include every 'selected' property / column in the group by` clause like you would in SQL.
You did not tell us what is the actual datatype of the ChartData, but from the error you are describing it looks like the problem is that whatever this datatype is it does not implement the IComparable interface which is a required interface if you want instances of the datatype to be comparable
I'm breaking my head with this and decided to share my problem with you
I want to create an anonymous select from several tables, some of them may contain more than one result. i want to concatenate these results into one string
i did something like this:
var resultTable = from item in dc.table
select new
{
id= item.id,
name= CreateString((from name in item.Ref_Items_Names
select name.Name).ToList()),
};
and the CreateString() is:
private string CreateString(List<string> list)
{
StringBuilder stringedData = new StringBuilder();
for (int i = 0; i < list.Count; i++)
{
stringedData.Append(list[i] + ", ");
}
return stringedData.ToString();
}
my intentions were to convert the "name" query to list and then sent it to CreateString() to convert it to one long concatenated string.
I tried using .Aggregate((current,next) => current + "," + next);
but when i try to convert my query to DataTable like below:
public DataTable ToDataTable(Object query)
{
DataTable dt = new DataTable();
IDbCommand cmd = dc.GetCommand(query as IQueryable);
SqlDataAdapter adapter = new SqlDataAdapter();
adapter.SelectCommand = (SqlCommand)cmd;
cmd.Connection.Open();
adapter.Fill(dt);
cmd.Connection.Close();
return dt;
}
I'm getting exception that "dc.GetCommand()" can't understand query with Aggregate method
later I tried to even use this simple query:
var resultTable = from itemin dc.table
select new
{
name = CreateString()
};
When CreateString() returns "success", nothing was inserted to "name"
why there is no way of using methods in select clause?
Thank you
Yotam
There is difference between LINQ to objects and LINQ to some-db-provider. Generally speaking, when using IQueryable, you can't use any methods, except the ones your provider understands.
What you can do is to retrieve the data from the database and then do the formatting using LINQ to objects:
var data = from item in dc.table
where /* some condition */
select item;
var result = from item in data.AsEnumerable()
select new
{
name = SomeFunction(item)
}
The AsEnumerable() extension method forces processing using LINQ to objects.
Forgive me if I've miss interpreted your question. It seems that what you are trying to do is abstract your select method for reuse. If this is the case, you may consider projection using a lambda expression. For example:
internal static class MyProjectors
{
internal static Expression<Func<Object1, ReturnObject>> StringDataProjector
{
get
{
return d => new Object1()
{
//assignment here
}
}
}
}
Now you can select your datasets as such:
dc.Table.Select(MyProjectors.StringDataProjector)
As for the concatenation logic, what about selecting to some base class with an IEnumerable<string> property and a read-only property to handle the concatenation of the string?