I am using a SQL query and then transforming the result using Hibernates's Transformers.aliasToBean().
One of the columns in my query is an enum. The transformation somehow fails for the enum. What should I do? Which datatype should I use? I want more than 1 character to transform the result into my enum type.
This is how the simplified version of my query/code looks like (b is an enum in the table profiles):
session.createSQLQuery("select a, b from profiles").setResultTransformer(Transformers.aliasToBean(Profile.class))
.list();
Exception : expected type: Foo.ProfileStateEnum, actual value: java.lang.Character
Assuming that the java enum type that corresponds to column b is Foo.ProfileStateEnum, the following code snippet should work for you. (I tested with Hibernate 4.1.6)
import java.util.Properties;
import org.hibernate.type.Type;
import org.hibernate.type.IntegerType;
import org.hibernate.internal.TypeLocatorImpl.TypeLocatorImpl;
import org.hibernate.type.TypeResolver.TypeResolver;
import org.hibernate.type.EnumType;
Properties params = new Properties();
params.put("enumClass", "Foo.ProfileStateEnum");
params.put("type", "12"); /*type 12 instructs to use the String representation of enum value*/
/*If you are using Hibernate 5.x then try:
params.put("useNamed", true);*/
Type myEnumType = new TypeLocatorImpl(new TypeResolver()).custom(EnumType.class, params);
List<Profile> profileList= getSession().createSQLQuery("select a as ID, b from profiles")
.addScalar("ID", IntegerType.INSTANCE)
.addScalar("b", myEnumType )
.setResultTransformer(Transformers.aliasToBean(Profile.class))
.list();
I found two ways to achieve it.
Use org.hibernate.type.CustomType with org.hibernate.type.EnumType(put either EnumType.NAMED or EnumType.TYPE, see EnumType#interpretParameters). Like below:
Properties parameters = new Properties();
parameters.put(EnumType.ENUM, MyEnum.class.getName());
// boolean or string type of true/false; declare database type
parameters.put(EnumType.NAMED, true);
// string only; declare database type
parameters.put(EnumType.TYPE, String.valueOf(Types.VARCHAR));
EnumType<MyEnum> enumType = new EnumType<>();
enumType.setTypeConfiguration(new TypeConfiguration());
enumType.setParameterValues(parameters);
CustomType customEnumType = new CustomType(enumType);
Another simple way. Use org.hibernate.type.StandardBasicTypeTemplate with org.hibernate.type.descriptor.sql.*TypeDescriptor. Like below:
StandardBasicTypeTemplate<MyEnum> enumType =
new StandardBasicTypeTemplate<>(VarcharTypeDescriptor.INSTANCE,
new EnumJavaTypeDescriptor<>(MyEnum.class));
Let's see why you are getting this exception.
From the question it is obvious that you have used #Enumerated(EnumType.STRING) annotation for the field 'b' in you model class. So the field is an enum for your model class and a varchar for your database. Native SQL is not concerned about you model class and returns what ever is there in the database table as it is. So in your case, the SQLQuery you are using will return a String for 'b' instead of a ProfileStateEnum type. But your setter method for 'b' in the Profile class takes a ProfileStateEnum type argument.
Thus you get the exception "expected type: Foo.ProfileStateEnum, actual value: java.lang.Character"
You can use Aliasing to solve the problem.
What I suggest is, alias your column with any name you want and create a setter method for that alias in your model/dto.
For example, lets alias your column as 'enumStr'.
Then your query will look like this : "select a, b as enumStr from profiles"
Now, create a setter method for that alias in the your Profile class.
(Assuming that the enum ProfileStateEnum can have any of the two values STATE1 and STATE2)
public void setEnumStr(String str){
/*Convert the string to enum and set the field 'b'*/
if(str.equals(ProfileStateEnum.STATE1.toString())){
b = ProfileStateEnum.STATE1;
} else {
b = ProfileStateEnum.STATE2;
}
}
Now on transforming, the setter for the alias setEnumStr(String) will be invoked instead of setter for the field setB(ProfileStateEnum) and the string will be converted and saved to the type you want without any exceptions.
I am a beginner in Hibernate and the solution worked for me. I am using PostgreSQL. But I believe it works for other databases too.
Related
I have a column title in a SQL table myTable.
Using Kotlin and JDBI, how would I go about getting all the distinct entries in this table?
This is what I have tried so far:
val jdbi = Jdbi.create("...url", "...user", "...password")
fun getTitles(): List<String> = jdbi.withHandleUnchecked { handle ->
handle.createQuery("select distinct(title) from myTable;")
.mapTo(String.javaClass)
.list()
However, this gives me the following exception:
A bean, Companion was mapped which was not instantiable (cannot find appropriate constructor)
What's going wrong here?
Apparently, String.javaClass is not what I want here (as it is a different type than is required). It is String::class.java.
What is a good way to query (always selecting all columns) and insert into arbitrary Oracle database tables using JDBC? I created the following method (haven't tested it yet) for retrieving any table's attribute names and types (I need the names for display purposes):
public ArrayList<Map<String, String>> retrieveTableAttributes(String tableName) throws SQLException{
ArrayList<Map<String, String>> attributes = new ArrayList<>();
DatabaseMetaData dbmd = conn.getMetaData();
ResultSet resultSet = dbmd.getColumns(null, null, tableName, null);
int i = 0;
while (resultSet.next()) {
attributes.add(new HashMap<String, String>());
attributes.get(i).put(resultSet.getString("COLUMN_NAME"), resultSet.getString("TYPE_NAME"));
i++;
}
resultSet.close();
return attributes;
}
I found this method PreparedStatement#setObject(int parameterIndex, Object x, int targetSqlType) which I think can be used to set a value for any arbitrary column type (in this case I would need to get the column type as an int instead of the type name), but I am not sure about this. So, is there a better way for setting and more importantly getting values from columns with arbitrary types? If it helps, I am trying to create a Java EE GUI tool for manipulating a database (adding, deleting, updating rows from any table in the database).
A simple method to get the type code from a named type using reflection:
public int getTypeByName(String name) {
for (Field field : java.sql.Types.class.getFields()) {
if (name.equalsIgnoreCase(field.getName())) return (Integer) field.get(null);
}
return -1;
}
Note that the TYPE_NAME column is probably not guaranteed to match Oracle's column support. A safer bet might just be to rely on the driver to make the right conversion choices using the untyped setObject and getObject methods.
I have an entity, with a field of type enum, that is persisted as an integer in my database.
When retrieving objects from the database using ICriteria, I wish to restrict the results to those with the field being a member of a collection of enum values. Does Restrictions.In work with a collection of enums?
The following does not work. Do I have to perform something like type-casting at the "restrictions.in" part of the query?
var myEnumCollection = new MyEnum[] { MyEnum.One };
return FindAll<MyType>(Restrictions.In("EnumProperty", myEnumCollection));
FindAll is a method encapsulating
criteria.GetExecutableCriteria(Session).List<MyType>()
My initial guess would be that you'll need to compare against the integer values of the enum members (assuming that you're mapping the enum as an integer); so something like:
var myEnumCollection = new int[] { MyEnum.One };
return FindAll<MyType>(Restrictions.In("EnumProperty", myEnumCollection));
May be the solution that you're after. If you update your post with further details (mapping of the enum member and the sql being generated by the query), I may be able to provide further assistance.
I have a column in my SQL-2005 database that used to be a varchar(max), but it has been changed to an nvarchar(max).
Now I need to update my hibernate mapping file to reflect the change, and this is what it used to be:
<element type="text" column="Value"/>
When I try to run the application, the following error appears:
org.hibernate.HibernateException: Wrong column type in [Table] for column Value. Found: ntext, expected: text
What should I put in the 'type' attribute to correctly map the column as an nvarchar(max)?
I've tried setting the type to ntext, but hibernate didn't know what that was. I tried setting the type to string, but it treated string as a text type.
What worked for me is to put the actual column definition in a #Column annotation:
#Column(name="requestXml", columnDefinition = "ntext")
private String request;
It can be fixed by
#Nationalized
annotation from hibernate, that marks a character data type like a nationalized variant (NVARCHAR, NCHAR, NCLOB, etc).
Found the answer at Tremend Tech Blog. You have to write your own SQLServerDialect class, it looks something like this:
public class SQLServerNativeDialect extends SQLServerDialect {
public SQLServerNativeDialect() {
super();
registerColumnType(Types.VARCHAR, "nvarchar($l)");
registerColumnType(Types.CLOB, "nvarchar(max)");
}
public String getTypeName(int code, int length, int precision, int scale) throws HibernateException {
if(code != 2005) {
return super.getTypeName(code, length, precision, scale);
} else {
return "ntext";
}
}
}
This class maps Hibernate's types to SQL types, so the class will map the nvarchar(max) SQL Data Type to Hibernate's CLOB data type.
The getTypeName method is used to return "ntext" when Hibernate asks about the data type with code 2005 (which looks like it's the nvarchar(max) data type).
Finally, you need to change your hibernate persistence dialect to this new SQLServerDialect class, which allows hibernate to translate data types into SQL data types.
I think it is
registerColumnType(Types.VARCHAR, "nvarchar($l)"); // l like _l_ength, not 1.
Using #Nationalized with length = Integer.MAX_VALUE should resolve the issue of NVARCHAR(MAX).
The entity class should somewhat like this
#Nationalized
#Column(length = Integer.MAX_VALUE)
private String nvarcharMax;
For more details checkout the documentation here
I want to run a query against two tables (which happen to be mapped in ActiveRecord). The query returns a result list that cannot be mapped to an ActiveRecord object (as it is custom aggregate information).
For instance
Dim query_str as string = "Select distinct d.ID, (select count(1) as exp from Sales_Leads where date_created <= :todays_date) as NbrLeads from Dealer d"
Dim q As Queries.HqlBasedQuery = New Queries.HqlBasedQuery(GetType(ICollection), query_str)
q.SetParameter("todays_date", DateTime.Today)
Dim i As ICollection = ActiveRecordMediator.ExecuteQuery(q)
What I'm looking for is simple execution of SQL, without an ActiveRecord object returned.
So, ideally, I'd be able to look at i("NbrResults") for each item in the collection.
The error I am getting is:
You have accessed an ActiveRecord
class that wasn't properly
initialized. The only explanation is
that the call to
ActiveRecordStarter.Initialize()
didn't include
System.Collections.ICollection class
Well, this was asked a long time ago but I have a working answer.
public static IList<T> ExecuteQuery<T>(HqlBasedQuery query)
where T : new()
{
query.SetResultTransformer(new NHibernate.Transform.AliasToBeanResultTransformer(typeof(T)));
var results = (ArrayList)ActiveRecordMediator.ExecuteQuery(query);
List<T> list = new List<T>(results.Count);
for (int i = 0; i < results.Count; i++)
{
list.Add((T)results[i]);
}
return list;
}
This will give you back results of type T. Type T can be anything you want. Type T needs a no argument constructor and it needs public fields or properties that match the column names or aliases in the query you build.
We do this all the time. Particularly when you want to use aggregate function in HQL to produce aggregate data.
A companion function will allow you to just pass in your query as a string as well as any positional parameters you might have:
public static IList<T> ExecuteQuery<T, U>(string hqlQuery, params object[] parameters)
where T : new()
{
return ExecuteQuery<T>(new HqlBasedQuery(typeof(U), hqlQuery, parameters));
}
Type U is any type that is a valid ActiveRecord type. It doesn't even have to be one of the types you are referencing. If you want you could replace it will some type you know is gonna be valid int he session and ditch the extra parameter.
Here was my final solution:
Dim query_str As String = "SELECT DISTINCT d.ID, count( l ) from LEAD as l join l.Dealer as d where l.DateCreated >= DATEADD(day, -30, :todays_date) GROUP BY d.ID"
Then obtain the active record session (or NHibernate, still don't even know what is returned here):
Dim sess As ISession = activerecordmediator.GetSessionFactoryHolder().CreateSession(GetType(ActiveRecordBase))
Dim q As NHibernate.IQuery = sess.CreateQuery(query_str)
q.SetParameter("todays_date", DateTime.Today)
Dim i As IList = q.List() ' get results
In the .aspx page, the result can be accessed in a GridView like so:
You're stepping outside the NHibernate paradigm to call down to SQL, which is somewhat against the spirit of ORM. It's not 'bad' per-se, but I'd certainly avoid breaking the abstraction if I could to try to maintain a looser coupling.
You can do what you want with a straight HQL query, which will return a collection of tuples containing the results of your query. I explained how to do this here
Custom query with Castle ActiveRecord
which you might want to have a look at. Even though you must specify a type when you new an HQLBasedQuery, NH is smart enough to know that if you don't select a type instance it should assemble a result-set based on object tuples.
(IMNSHO it's still a bit non-pure - I'd be tempted to try to model this relationship as an object and map it accordingly, but then I'd have to bash the DB into shape to suit the object model and that's not going to fly in all cases.)