JPA2 CriteriaBuilder: Using LOB property for greaterThan comparison - sql-server

My application is using SQLServer and JPA2 in the backend. App makes use of a timestamp column (in the SQLServer sense, which is equivalent to row version see here) per entity to keep track of freshly modified entities. NB SQLServer stores this column as binary(8).
Each entity has a respective timestamp property, mapped as #Lob, which is the way to go for binary columns:
#Lob
#Column(columnDefinition="timestamp", insertable=false, updatable=false)
public byte[] getTimestamp() {
...
The server sends incremental updates to mobile clients along with the latest database timestamp. The mobile client will then pass the old timestamp back to the server on the next refresh request so that the server knows to return only fresh data. Here's what a typical query (in JPQL) looks like:
select v from Visit v where v.timestamp > :oldTimestamp
Please note that I'm using a byte array as a query parameter and it works fine when implemented in JPQL this way.
My problems begin when trying to do the same using the Criteria API:
private void getFreshVisits(byte[] oldVersion) {
EntityManager em = getEntityManager();
CriteriaQuery<Visit> cq = cb.createQuery(Visit.class);
Root<Visit> root = cq.from(Visit.class);
Predicate tsPred = cb.gt(root.get("timestamp").as(byte[].class), oldVersion); // compiler error
cq.where(tsPred);
...
}
The above will result in compiler error as it requires that the gt method used strictly with Number. One could instead use the greaterThan method which simply requires the params to be Comparable and that would result in yet another compiler error.
So to sum it up, my question is: how can I use the criteria api to add a greaterThan predicate for a byte[] property? Any help will be greatly appreciated.
PS. As to why I'm not using a regular DateTime last_modified column: because of concurrency and the way synchronization is implemented, this approach could result in lost updates. Microsoft's Sync Framework documentation recommends the former approach as well.

I know this was asked a couple of years back but just in case anyone else stumbles upon this.. In order to use a SQLServer rowver column within JPA you need to do a couple of things..
Create a type that will wrap the rowver/timestamp:
import com.fasterxml.jackson.annotation.JsonIgnore;
import javax.xml.bind.annotation.XmlTransient;
import java.io.Serializable;
import java.math.BigInteger;
import java.util.Arrays;
/**
* A RowVersion object
*/
public class RowVersion implements Serializable, Comparable<RowVersion> {
#XmlTransient
#JsonIgnore
private byte[] rowver;
public RowVersion() {
}
public RowVersion(byte[] internal) {
this.rowver = internal;
}
#XmlTransient
#JsonIgnore
public byte[] getRowver() {
return rowver;
}
public void setRowver(byte[] rowver) {
this.rowver = rowver;
}
#Override
public int compareTo(RowVersion o) {
return new BigInteger(1, rowver).compareTo(new BigInteger(1, o.getRowver()));
}
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
RowVersion that = (RowVersion) o;
return Arrays.equals(rowver, that.rowver);
}
#Override
public int hashCode() {
return Arrays.hashCode(rowver);
}
}
The key here is that it implement Comparable if you want to use it in calculations (which you definitely do)..
Next create a AttributeConverter that will move from a byte[] to the class you just made:
import javax.persistence.AttributeConverter;
import javax.persistence.Converter;
/**
* JPA converter for the RowVersion type
*/
#Converter
public class RowVersionTypeConverter implements AttributeConverter<RowVersion, byte[]> {
#Override
public byte[] convertToDatabaseColumn(RowVersion attribute) {
return attribute != null ? attribute.getRowver() : null;
}
#Override
public RowVersion convertToEntityAttribute(byte[] dbData) {
return new RowVersion(dbData);
}
}
Now let's apply this RowVersion attribute/type to a real world scenario. Let's say you wanted to find all Programs that have changed on or before some point in time.
One straightforward way to solve this would be to use a DateTime field in the object and timestamp column within db. Then you would use 'where lastUpdatedDate <= :date'.
Suppose that you don't have that timestamp column or there's no guarantee that it will be updated properly when changes are made; or let's say your shop loves SQLServer and wants to use rowver instead.
What to do? There are two issues to solve.. one how to generate a rowver and two is how to use the generated rowver to find Programs.
Since the database generates the rowver, you can either ask the db for the 'current max rowver' (a custom sql server thing) or you can simply save an object that has a RowVersion attribute and then use that object's generated RowVersion as the boundary for the query to find the Programs changed after that time. The latter solution is more portable is what the solution is below.
The SyncPoint class snippet below is the object that is used as a 'point in time' kind of deal. So once a SyncPoint is saved, the RowVersion attached to it is the db version at the time it was saved.
Here is the SyncPoint snippet. Notice the annotation to specify the custom converter (don't forget to make the column insertable = false, updateable = false):
/**
* A sample super class that uses RowVersion
*/
#MappedSuperclass
public abstract class SyncPoint {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
// type is rowver for SQLServer, blob(8) for postgresql and h2
#Column(name = "current_database_version", insertable = false, updatable = false)
#Convert(converter = RowVersionTypeConverter.class)
private RowVersion currentDatabaseVersion;
#Column(name = "created_date_utc", columnDefinition = "timestamp", nullable = false)
private DateTime createdDate;
...
Also (for this example) here is the Program object we want to find:
#Entity
#Table(name = "program_table")
public class Program {
#Id
private Integer id;
private boolean active;
// type is rowver for SQLServer, blob(8) for postgresql and h2
#Column(name = "rowver", insertable = false, updatable = false)
#Convert(converter = RowVersionTypeConverter.class)
private RowVersion currentDatabaseVersion;
#Column(name = "last_chng_dt")
private DateTime lastUpdatedDate;
...
Now you can use these fields within your JPA criteria queries just like anything else.. here is a snippet that we used inside a spring-data Specifications class:
/**
* Find Programs changed after a synchronization point
*
* #param filter that has the changedAfter sync point
* #return a specification or null
*/
public Specification<Program> changedBeforeOrEqualTo(final ProgramSearchFilter filter) {
return new Specification<Program>() {
#Override
public Predicate toPredicate(Root<Program> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
if (filter != null && filter.changedAfter() != null) {
// load the SyncPoint from the db to get the rowver column populated
SyncPoint fromDb = synchronizationPersistence.reload(filter.changedBeforeOrEqualTo());
if (fromDb != null) {
// real sync point made by database
if (fromDb.getCurrentDatabaseVersion() != null) {
// use binary version
return cb.lessThanOrEqualTo(root.get(Program_.currentDatabaseVersion),
fromDb.getCurrentDatabaseVersion());
} else if (fromDb.getCreatedDate() != null) {
// use timestamp instead of binary version cause db doesn't make one
return cb.lessThanOrEqualTo(root.get(Program_.lastUpdatedDate),
fromDb.getCreatedDate());
}
}
}
return null;
}
};
}
The specification above works with both the binary current database version or a timestamp.. this way I could test my stuff and all the upstream code on a database other than SQLServer.
That's it really: a) type to wrap the byte[] b) JPA converter c) use attribute in query.

Related

Room Data Base Create Instance

I want to Create An Instance Of Room Data base in Composable
But
val db = Room.databaseBuilder(applicationContext, UserDatabase::class.java,"users.db").build()
is not working here not getting applicationContext
How to create an instance of context in composable
Have you tried getting the context with : val context = LocalContext.current and then adding this to get your applicationContext?
Like this: context.applicationContext or using simply val db = Room.databaseBuilder(context, UserDatabase::class.java,"users.db").build()
Room (and the underlying SQliteOpenHelper) only need the context to open the database (or more correctly to instantiate the underlying SQLiteOpenHelper).
Room/Android SQLiteOpenHelper uses the context to ascertain the Application's standard (recommended) location (data/data/<the_package_name>/databases). e.g. in the following demo (via Device Explorer):-
The database, as it is still open includes 3 files (the -wal and -shm are the Write Ahead Logging files that will at sometime be committed/written to the actual database (SQLite handles that)).
so roughly speaking Room only needs to have the context so that it can ascertain /data/data/a.a.so75008030kotlinroomgetinstancewithoutcontext/databases/testit.db (in the case of the demo).
So if you cannot use the applicationContext method then you can circumvent the need to provide the context, if using a singleton approach AND if after instantiating the singleton.
Perhaps consider this demo:-
First some pretty basic DB Stuff (table (#Entity annotated class), DAO functions and #Database annotated abstract class WITH singleton approach). BUT with some additional functions for accessing the instance without the context.
#Entity
data class TestIt(
#PrimaryKey
val testIt_id: Long?=null,
val testIt_name: String
)
#Dao
interface DAOs {
#Insert(onConflict = OnConflictStrategy.IGNORE)
fun insert(testIt: TestIt): Long
#Query("SELECT * FROM testit")
fun getAllTestItRows(): List<TestIt>
}
#Database(entities = [TestIt::class], exportSchema = false, version = 1)
abstract class TestItDatabase: RoomDatabase() {
abstract fun getDAOs(): DAOs
companion object {
private var instance: TestItDatabase?=null
/* Extra/not typical for without a context (if wanted)*/
fun isInstanceWithoutContextAvailable() : Boolean {
return instance != null
}
/******************************************************/
/* Extra/not typical for without a context */
/******************************************************/
fun getInstanceWithoutContext(): TestItDatabase? {
if (instance != null) {
return instance as TestItDatabase
}
return null
}
/* Typically the only function*/
fun getInstance(context: Context): TestItDatabase {
if (instance==null) {
instance = Room.databaseBuilder(context,TestItDatabase::class.java,"testit.db")
.allowMainThreadQueries() /* for convenience/brevity of demo */
.build()
}
return instance as TestItDatabase
}
}
}
And to demonstrate (within an activity for brevity) :-
class MainActivity : AppCompatActivity() {
lateinit var roomInstance: TestItDatabase
lateinit var dao: DAOs
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
roomInstance = TestItDatabase.getInstance(this) /* MUST be used before withoutContext functions but could be elsewhere shown here for brevity */
dao = roomInstance.getDAOs()
//dao.insert(TestIt(testIt_name = "New001")) /* Removed to test actually doing the database open with the without context */
logDataWithoutContext()
addRowWithoutContext()
addRowWithApplicationContext()
logDataWithoutContext()
}
private fun logDataWithoutContext() {
Log.d("${TAG}_LDWC","Room DB Instantiated = ${TestItDatabase.isInstanceWithoutContextAvailable()}")
for (t in TestItDatabase.getInstanceWithoutContext()!!.getDAOs().getAllTestItRows()) {
Log.d("${TAG}_LDWC_DATA","TestIt Name is ${t.testIt_name} ID is ${t.testIt_id}")
}
}
private fun addRowWithoutContext() {
Log.d("${TAG}_LDWC","Room DB Instantiated = ${TestItDatabase.isInstanceWithoutContextAvailable()}")
if (TestItDatabase.getInstanceWithoutContext()!!.getDAOs()
.insert(TestIt(System.currentTimeMillis(),"NEW AS PER ID (the time to millis) WITHOUT CONTEXT")) > 0) {
Log.d("${TAG}_ARWC_OK","Row successfully inserted.")
} else {
Log.d("${TAG}_ARWC_OUCH","Row was not successfully inserted (duplicate ID)")
}
}
private fun addRowWithApplicationContext() {
TestItDatabase.getInstance(applicationContext).getDAOs().insert(TestIt(System.currentTimeMillis() / 1000,"NEW AS PER ID (the time to seconds) WITH CONTEXT"))
}
}
The result output to the log showing that the database access, either way, worked:-
2023-01-05 12:45:39.020 D/DBINFO_LDWC: Room DB Instantiated = true
2023-01-05 12:45:39.074 D/DBINFO_LDWC: Room DB Instantiated = true
2023-01-05 12:45:39.077 D/DBINFO_ARWC_OK: Row successfully inserted.
2023-01-05 12:45:39.096 D/DBINFO_LDWC: Room DB Instantiated = true
2023-01-05 12:45:39.098 D/DBINFO_LDWC_DATA: TestIt Name is NEW AS PER ID (the time to seconds) WITH CONTEXT ID is 1672883139
2023-01-05 12:45:39.098 D/DBINFO_LDWC_DATA: TestIt Name is NEW AS PER ID (the time to millis) WITHOUT CONTEXT ID is 1672883139075
note that the shorter id was the last added but appears first due to it being selected first as it appears earlier in the index that the SQlite Query Optimiser would have used (aka the Primary Key).
basically the same date time second wise but the first insert included milliseconds whilst the insert via AddRowWithApplicationContext drops the milliseconds.

SQLite Xamarin PCL

I am developing an App in Xamarin type PCL, for my DB structure, I want to use SQLite, but I have the following doubts ...
When entering a record in my DB, it takes the ID = 0, in my data model use
[PrimaryKey, AutoIncrement]
Public int ViolationID {get; set; }
And still, I enter the registry at zero, I do not know I'm doing wrong ... or is this a bug in the SQLite.NET-PCL package?
How can I verify that these records are actually being entered? I have in my code
public class DataAccess : IDisposable
{
private SQLiteConnection connection;
public DataAccess()
{
var entity = DependencyService.Get<IEntity>();
connection = new SQLiteConnection(entity.Plataforma, System.IO.Path.Combine(entity.DirectorioBD, "Infraccions.db3"));
connection.CreateTable<Infraccion>();
}
public void InsertInfraccion(Infraccion infraccion)
{
connection.Insert(infraccion);
}
public void UpdateInfraccion(Infraccion infraccion)
{
connection.Update(infraccion);
}
public Infraccion GetInfraccion(int InfraccionID)
{
return connection.Table<Infraccion>().FirstOrDefault(c => c.InfraccionID == InfraccionID);
}
public List<Infraccion> GetInfraccions()
{
return connection.Table<Infraccion>().OrderBy(c => c.MotivoID).ToList();
}
public void DeleteInfraccion(Infraccion infraccion)
{
connection.Delete(infraccion);
}
public void Dispose()
{
connection.Dispose();
}
}
Should I create a table called Infraccions.db3 on my phone?
Thank you for your comments...
Are you saying that all new records have an ID of 0 and overwrite the existing record in the database?
If so, then this is how SQLite works - for int columns 0 is a valid value, so when the ID is 0 it will overwrite the record, instead of incrementing the value.
The correct way to use int primary keys is to define your primary key as a nullable int, that way the value for a new record is null, which will be updated to the next available id:
[PrimaryKey, AutoIncrement]
public int? ViolationID {get; set; }
Essentially change int to int?.
1) When entering a record in my DB, it takes the ID = 0, in my data
model use
You are using primary key and auto increment in your model that's means you are not able to enter 0 manually in the primary field and it takes automatically next value in this field.
2) How can I verify that these records are actually being entered?
You can get DB file path when you create your database and you can able to open and see that data.
(System.IO.Path.Combine(entity.DirectorioBD, "Infraccions.db3") )
There are many browser plugins to access the sqllite database.

Cannot Pass Null Value to Custom Aggregate

Afternoon,
I'm writing a custom median function (without looking at existing solutions, i like the challenge), after lots of fiddling I'm most of the way there. I cannot however pass in a column that contains a null value. I'm handling this in the c# Code but it seems to be being stopped by SQL before it gets there.
You get this error...
Msg 6569, Level 16, State 1, Line 11 'Median' failed because parameter 1 is not allowed to be null.
C#:
namespace SQLMedianAggregate
{
[System.Serializable]
[Microsoft.SqlServer.Server.SqlUserDefinedAggregate(
Microsoft.SqlServer.Server.Format.UserDefined,
IsInvariantToDuplicates = false, // duplicates may change results
IsInvariantToNulls = true, // receiving a NULL is handled later in code
IsInvariantToOrder = true, // is sorted later
IsNullIfEmpty = true, // if no values are given the result is null
MaxByteSize = -1,
Name = "Median" // name of the aggregate
)]
public struct Median : IBinarySerialize
{
public double Result { get; private set; }
public bool HasValue { get; private set; }
public DataTable DT_Values { get; private set; } //only exists for merge essentially
public static DataTable DT_Final { get; private set; } //Need a static version so its accesible within terminate
public void Init()
{
Result = double.NaN;
HasValue = false;
DT_Values = new DataTable();
DT_Values.Columns.Add("Values", typeof(double));
DT_Final = new DataTable();
DT_Final.Columns.Add("Values", typeof(double));
}
public void Accumulate(double number)
{
if (double.IsNaN(number))
{
//skip
}
else
{
//add to tables
DataRow NR = DT_Values.NewRow();
NR[0] = number;
DT_Values.Rows.Add(NR);
DataRow NR2 = DT_Final.NewRow();
NR2[0] = number;
DT_Final.Rows.Add(NR2);
HasValue = true;
}
}
public void Merge(Median group)
{
// Count the product only if the other group has values
if (group.HasValue)
{
DT_Final.Merge(group.DT_Values);
//DT_Final = DT_Values;
}
}
public double Terminate()
{
if (DT_Final.Rows.Count == 0) //Just to handle roll up so it doesn't crash (doesnt actually work
{
DataRow DR = DT_Final.NewRow();
DR[0] = 0;
DT_Final.Rows.Add(DR);
}
//Sort Results
DataView DV = DT_Final.DefaultView;
DV.Sort = "Values asc";
DataTable DTF = new DataTable();
DTF = DV.ToTable();
////Calculate median and submit result
double MiddleRow = (DT_Final.Rows.Count -1.0) / 2.0;
if (MiddleRow % 2 != 0)
{
double upper = (double)(DT_Final.Rows[Convert.ToInt32(Math.Ceiling(MiddleRow))]["Values"]);
double lower = (double)(DT_Final.Rows[Convert.ToInt32(Math.Floor(MiddleRow))]["Values"]);
Result = lower + ((upper - lower) / 2);
} else
{
Result = (double)(DT_Final.Rows[Convert.ToInt32(MiddleRow)]["Values"]);
}
return Result;
}
public void Read(BinaryReader SerializationReader)
{
//Needed to get this working for some reason
}
public void Write(BinaryWriter SerializationWriter)
{
//Needed to get this working for some reason
}
}
}
SQL:
DROP AGGREGATE dbo.Median
DROP ASSEMBLY MedianAggregate
CREATE ASSEMBLY MedianAggregate
AUTHORIZATION dbo
FROM 'C:\Users\#######\Documents\Visual Studio 2017\Projects\SQLMedianAggregate\SQLMedianAggregate\bin\Debug\SQLMedianAggregate.dll'
WITH PERMISSION_SET = UNSAFE;
CREATE AGGREGATE dbo.Median (#number FLOAT) RETURNS FLOAT
EXTERNAL NAME [MedianAggregate]."SQLMedianAggregate.Median";
Any ideas of what setting or code i'm missing that will allow this. I pretty much just want it to ignore nulls.
SQL Version is SQL2008 R2 btw
The problem is your datatype. You need to use the Sql* types for SQLCLR parameters, return values, and result set columns. In this case, you need to change:
Accumulate(double number)
into:
Accumulate(SqlDouble number)
Then, you access the double value using the Value property that all Sql* types have (i.e. number.Value in this case).
And then, at the beginning of the Accumulate method, you need to check for NULL using the IsNull property:
if (number.IsNull)
{
return;
}
Also, for more information on using SQLCLR in general, please see the series I am writing on this topic on SQL Server Central: Stairway to SQLCLR (free registration is required to read content on that site, but it's worth it :-).
And, since we are talking about median calculations here, please see the article I wrote (also on SQL Server Central) on the topic of UDAs and UDTs that uses Median as the example: Getting The Most Out of SQL Server 2005 UDTs and UDAs. Please keep in mind that the article was written for SQL Server 2005 which has a hard limit of 8000 bytes of memory for UDTs and UDAs. That limit was lifted in SQL Server 2008, so rather than using the compression technique shown in that article, you could simply set MaxByteSize in the SqlUserDefinedAggregate to -1 (as you are currently doing) or SqlMetaData.MaxSize (or something very close to that).
Also, DataTable is a bit heavy-handed for this type of operation. All you need is a simple List<Double> :-).
Regarding the following line of code (broken into 2 lines here to prevent the need to scroll):
public static DataTable DT_Final { get; private set; }
//Need a static version so its accesible within terminate
This is a huge misunderstanding of how UDAs and UDTs work. Please do NOT use static variables here. Static variables are shared across Sessions, hence your current approach is not thread-safe. So you would either get errors about it already being declared or various Sessions would alter the value unbeknownst to other Sessions, as they would all share the single instance of
DT_Final. And the errors and/or odd behavior (i.e. erroneous results that you can't debug) might happen in a single session if a parallel plan is used.
UDTs and UDAs get serialized to a binary value stored in memory, and then are deserialized which keeps their state intact. This is the reason for the Read and Write methods, and why you needed to get those working.
Again, you don't need (or want) DataTables here as they are over-complicating the operation and take up more memory than is ideal. Please see the article I linked above on UDAs and UDTs to see how the Median operation (and UDAs in general) should work.

stored procedure 'auto_pk_for_table' not found

I don't know why I received the error :
org.apache.cayenne.CayenneRuntimeException: [v.4.0.M5 Feb 24 2017 07:47:55] Commit Exception
[...]
Caused by: java.sql.SQLException: Procédure stockée 'auto_pk_for_table' introuvable.
[...]
I'm using Cayenne :
<dependency>
<groupId>org.apache.cayenne</groupId>
<artifactId>cayenne-server</artifactId>
<version>4.0.M5</version>
</dependency>
and JDTS for sql server :
<dependency>
<groupId>net.sourceforge.jtds</groupId>
<artifactId>jtds</artifactId>
<version>1.3.1</version>
</dependency>
The connexion is ok :
avr. 10, 2017 2:36:30 PM org.apache.cayenne.datasource.DriverDataSource getConnection
INFOS: +++ Connecting: SUCCESS.
I'm trying to create a new user (I'm starting by bascis!) so my code is :
(I cut a little bit, it's too long:!)
public abstract class _UserInfo extends CayenneDataObject {
public static final String ADDRESS_PROPERTY = "address";
public void setAddress(String address) {
writeProperty(ADDRESS_PROPERTY, address);
}
public String getAddress() {
return (String)readProperty(ADDRESS_PROPERTY);
}
}
public class UserInfo extends _UserInfo implements Serializable {
private static final long serialVersionUID = 1L;
public String address;
public String getAdress() {
return address;
}
public void setAddress(String address) {
super.setAddress(address);
}
//I have the hashcode and equals too
}
Then, I used vaadin to create my form :
public class UserAddView extends CustomComponent implements View {
private static final long serialVersionUID = 1L;
private TextField address;
private Button save;
public static final String USERVIEW = "user";
public boolean checkValidation() {
if (!checkTextFieldValid(address))
return false;
return true;
}
public boolean checkTextFieldValid(TextField element) {
if (element == null || element.isEmpty()) {
Notification.show(
"You should register a " + element.getDescription(),
Type.WARNING_MESSAGE);
return false;
}
return true;
}
public UserAddView() {
VerticalLayout mainLayout = new VerticalLayout();
mainLayout.setSizeFull();
setCompositionRoot(mainLayout);
final VerticalLayout vlayout = new VerticalLayout();
address = new TextField("Address:");
address.setDescription("Address");
vlayout.addComponent(address);
save = new Button("Save");
vlayout.addComponent(save);
mainLayout.addComponent(new HeaderMenu());
mainLayout.addComponent(vlayout);
addListeners();
}
private void addListeners() {
save.addClickListener(new ClickListener() {
private static final long serialVersionUID = 1L;
#Override
public void buttonClick(ClickEvent event) {
if (checkValidation() == true) {
ServerRuntime cayenneRuntime = ServerRuntime.builder()
.addConfig("cayenne-myapplication.xml").build();
ObjectContext context = cayenneRuntime.newContext();
UserInfo user = context.newObject(UserInfo.class);
user.setAddress(address.getValue());
user.getObjectContext().commitChanges();
Notification.show(
"Has been saved, We will send you your password by email. Your user login is: "
+ email.getValue(), Type.TRAY_NOTIFICATION);
getUI().getNavigator().navigateTo(HomepageView.MAINVIEW);
}
}
});
}
#Override
public void enter(ViewChangeEvent event) {
// TODO Auto-generated method stub
}
}
EDIT, add information : In my user object, I have a userid (primary key), in cayenne I wrote it as primary key too and in smallint. This error seems to be link... https://cayenne.apache.org/docs/3.1/api/org/apache/cayenne/dba/sybase/SybasePkGenerator.html
The error happens when you insert a new object. For each new object Cayenne needs to generate a value of the primary key. There are various strategies to do this. The default strategy depends on the DB that you are using. For SQLServer (and for Sybase, as you've discovered :)) that strategy is to use a special stored procedure.
To create this stored procedure (and other supporting DB objects), go to CayenneModeler, open your project, and select "Tools > Generate Database Schema". In "SQL Options" tab, uncheck all checkboxes except for "Create Primary Key Support". The SQL you will see in the window below the checkboxes is what you need to run on SQL server. Either do it from Cayenne modeler or copy/paste to your favorite DB management tool.
There's also an alternative that does not require a stored procedure - using DB auto-increment feature. For this you will need to go to each DbEntity in the Modeler and under the "Entity" tab select "Database-Generated" in the "Pk Generation Strategy" dropdown. This of course implies that your PK column is indeed an auto-increment in the DB (meaning you may need to adjust your DB schema accordingly).

Map null column as 0 in a legacy database (JPA)

Using Play! framework and it's JPASupport class I have run into a problem with a legacy database.
I have the following class:
#Entity
#Table(name="product_catalog")
public class ProductCatalog extends JPASupport {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
public Integer product_catalog;
#OneToOne
#JoinColumn(name="upper_catalog")
public ProductCatalog upper_catalog;
public String name;
}
Some product catalogs don't have an upper catalog, and this is referenced as 0 in a legacy database. If I supply the upper_catalog as NULL, then expectedly JPA inserts a NULL value to that database column.
How could I force the null values to be 0 when writing to the database and the other way around when reading from the database?
I don't see any easy way of achieving what you want with JPA directly (and there are great chance that even if you find a way that works with basic operation like save or load, that it will not work with more complex use case, like complex criteria / hql, none standard fetching mode, etc)
So i would do that :
#Entity
#Table(name="product_catalog")
public class ProductCatalog extends JPASupport {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
public Integer product_catalog;
#Column(name="upper_catalog")
public Long upper_catalog_id;
public String name;
public ProductCatalog getUpperCatalog() {
if (upper_catalog_id == 0)
return null;
return ProductCatalog.findById(upper_catalog_id);
}
public void setUpperCatalog(ProductCatalog pc) {
if (pc == null) {
upper_catalog_id = 0;
}
else {
if (pc.id == null) {
// option 1. a bit like a cascade
pc.save();
// option 2. if you consider passing a transient entity is not valid
throw new RuntimeException("transient entity " + pc.toString());
}
upper_catalog_id = pc.id;
}
}
}
I see two options:
Use a primitive data type as Id (i.e. int instead of Integer)
If you are using Hibernate as JPA provider, use a CustomType to do the conversion

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