I'm trying to query abstract entity using SqlQuery() method (code first).
public abstract class UserComment
{
... [internals]
}
public class BlogComment : UserComment
{
... [internals]
}
var result = Context.Database.SqlQuery<UserComment>(
#"select * from [UserComments] where ... [internals]",
new SqlParameter("user_id", user.Id));
This gives me error:
System.ArgumentNullException: Value cannot be null.
Parameter name: constructor
If I change abstract type to concrete..
Context.Database.SqlQuery<BlogComment>
...everything works fine.
Is it possible to query abstract class using raw queries?
I didn't try it but I expect the answer is no. You cannot create instance of abstract class and that is exactly what EF is trying to do when materializing result set of the raw query.
Related
I have a Card entity class with many columns.
I used dto because I want to get some columns from this Entity.
I created a DTO class and wrote a query to CardRepositoryCustom.
But when I try to run the Query I get various errors "No constructor taking".
My dto class:
#Data
#NoArgsConstructor
#AllArgsConstructor
public class CardDTO {
private String test1;
private String test2;
private String test3;
private String test4;
}
JPQL RepositoryCustom :
#Repository
#Transactional
public class CardRepositoryCustom {
public CardDTO test1() {
JpaResultMapper jpaResultMapper = new JpaResultMapper();
String q = "SELECT "+
" c.test1 "+
"FROM "+
" CardEntity c ";
Query query = entityManager.createQuery(q);
try {
return jpaResultMapper.uniqueResult(query, CardDTO.class);
} catch (NoResultException nre) {
return null;
}
}
}
Errors:
java.lang.RuntimeException: No constructor taking: java.lang.String
at org.qlrm.mapper.JpaResultMapper.findConstructor(JpaResultMapper.java:107) ~[qlrm-1.7.1.jar:na]
at org.qlrm.mapper.JpaResultMapper.uniqueResult(JpaResultMapper.java:64) ~[qlrm-1.7.1.jar:na]
at ....
I know how to fix this error.
You just need to write the following constructor in the DTO class as shown below.
public CardDTO(String test1) {
this.setTest1(test1);
}
Here I am curious, if I want test2, test3, test4 and write Query in Custom class, should there be as many constructors in DTO class as that number?
I think this method is really inefficient. Is there any solution I am not aware of?
This seems to be more about QLRM than JPA or Spring.
Judging from the error message the constructor has to match the arguments provided. Probably the easiest variant is to always provide all arguments, possibly with a value of null or some other literal.
The query in your example would then become.
SELECT c.test1, null, null, null FROM CardEntity c
Of course QLRM just provides a JpaResultMapper and it would probably not too difficult to provide your own, or offer a PR to QLRM that inspects names of the result set and tries to match them to parameter names or the constructor.
Ok, hope to not get too many flags, but it's to annoying.
I have a method in my controller which calls a method from another class:
offerForCreate.Rating = CalculateRating.CreateRating(addOffer);
and entire called class :
public class CalculateRating
{
private readonly DataContext mainContext;
public CalculateRating(DataContext mainContext)
{
this.mainContext = mainContext;
}
// calcul rating oferte noi
public decimal CreateRating(OfferForCreate offer)
{
decimal rating = mainContext.Database.FromSql<decimal>("RatingCalculator", offer.locationId, offer.typeId);
return rating;
}
}
I get an error when try to execute this procedure:
Error CS1061: 'DatabaseFacade' does not contain a definition for 'FromSql' and no extension method 'FromSql' accepting a first argument of type 'DatabaseFacade' could be found
and another if I don't create an instance of CalculateRating class in my controller :
Controllers\AnnouncesController.cs(127,37): error CS0120: An object reference is required for the non-static field, method, or property 'CalculateRating.CreateRating(OfferForCreate)
Everywhere I see must specify the entity, but what entity I can specify if my stored procedure use multiple tables?
Asp.Net Core Web API
You can execute stored proc like this:
using (var command = mainContext.Database.GetDbConnection().CreateCommand())
{
command.CommandType = System.Data.CommandType.StoredProcedure;
command.CommandText = "dbo.RatingCalculator";
var locationIdParam = new System.Data.SqlClient.SqlParameter("#locationId", System.Data.SqlDbType.Int);
locationIdParam .Value = offer.locationId;
//DO same for typeId parameter
//Params to Parameters collection
command.Parameters.Add(locationIdParam);
command.Connection.Open();
return (double)command.ExecuteScalar();
}
Controllers\AnnouncesController.cs(127,37): error CS0120: An object reference is required for the non-static field, method, or property 'CalculateRating.CreateRating(OfferForCreate)
This error is occuring because if you declare CalculateRating as static you can not reference in non-static field mainContext.
You should create an instance of your CalculateRating class using Dependency Injection. Here are steps:
Create an interface ICalculateRating
public interface ICalculateRating {
decimal CreateRating(OfferForCreate offer);
}
Update CalculateRating class to implement ICalculateRating
Register the DBContext and ICalculateRating mappings in ConfigureServices method of Startup.cs file like this:
services.AddDbContext<DbContext>(opts=> { opts.UseSqlServer("sqlserver conntection string") }, ServiceLifetime.Scoped);
services.AddTransient<ICalculateRating, CalculateRating>();
In your controller constructor, input an argument of type ICalculateRating which will be injected by Microsoft Dependency Injection framework at runtime:
private readonly ICalculateRating _calculateRating;
public MyController(ICalculateRating calculateRating) {
_calculateRating = calculateRating;
}
You can then call the method like this:
offerForCreate.Rating = _calculateRating.CreateRating(addOffer);
Here is my entity class:
public class User {
#Id
UserIdentifier userIdentifier;
String name;
}
public class UserIdentifier {
String ssn;
String id;
}
Here is what I am trying to do:
public interface UserRepository extends MongoRepository<User, UserIdentifier>
{
User findBySsn(String ssn);
}
I get an exception message (runtime) saying:
No property ssn found on User!
How can I implement/declare such a query?
According to Spring Data Repositories reference:
Property expressions can refer only to a direct property of the managed entity, as shown in the preceding example. At query creation time you already make sure that the parsed property is a property of the managed domain class. However, you can also define constraints by traversing nested properties.
So, instead of
User findBySsn(String ssn);
the following worked (in my example):
User findByUserIdentifierSsn(String ssn);
Is there any sample Scala code available for creating stored procedures in Neo4j-3.0.3 ?
I have been trying to create one simple Scala based stored procedure. Below is the Error message I get when I copy my scala-jar file to the neo4j-plugins directory and start the neo4j server :
=================
Caused by: org.neo4j.kernel.lifecycle.LifecycleException: Component 'org.neo4j.kernel.impl.proc.Procedures#1ac0223' was successfully initialized, but failed to start. Please see attached cause exception.
at org.neo4j.kernel.lifecycle.LifeSupport$LifecycleInstance.start(LifeSupport.java:444)
at org.neo4j.kernel.lifecycle.LifeSupport.start(LifeSupport.java:107)
at org.neo4j.kernel.impl.factory.GraphDatabaseFacadeFactory.newFacade(GraphDatabaseFacadeFactory.java:140)
... 10 more
Caused by: org.neo4j.kernel.api.exceptions.ProcedureException: Unable to find a usable public no-argument constructor in the class `neoscala`. Please add a valid, public constructor, recompile the class and try again.
=================
The scala class that I have used is :
package neoproc
import org.neo4j.graphdb.GraphDatabaseService
import org.neo4j.procedure.Procedure;
import javax.ws.rs.core.{Context, Response}
class neoscala(#Context db: GraphDatabaseService) {
#Procedure
def alice():String = {
String.valueOf(db.execute( "MATCH (n:User) return n" ));
}
}
Your Scala class declares a constructor with a GraphDatabaseService argument, and the exception tells you that it only wants a no-argument constructor.
It's documented in both
the user documentation:
Only static fields and #Context-annotated fields are allowed in Procedure classes.
the Javadoc:
The procedure method itself can contain arbitrary Java code - but in order to work with the underlying graph, it must have access to the graph API. This is done by declaring fields in the procedure class, and annotating them with the Context annotation. Fields declared this way are automatically injected with the requested resource. This is how procedures gain access to APIs to do work with.
All fields in the class containing the procedure declaration must either be static; or it must be public, non-final and annotated with Context.
Apparently it's not possible to create a class with a public field in Scala, so you'll have to create a parent Java class with the public field, and extend it with your Scala class:
// ProcedureAdapter.java
public abstract class ScalaProcedureAdapter {
#Context
public GraphDatabaseService db;
}
// neoscala.scala
class neoscala extends ScalaProcedureAdapter {
// ...
}
Here is the solution for this :
We will create Class in scala :
class FullTextIndex extends JavaHelper {
#Procedure("example.search")
#PerformsWrites
def search(#Name("label") label: String,
#Name("query") query: String): Stream[SearchHit] = {
//declare your method
}
val nodes: Stream[Node] = db.index.forNodes(index).query(query).stream
val newFunction: java.util.function.Function[Node, SearchHit] = (node: Node) => new SearchHit(node)
nodes.map {
newFunction
}
}
private def indexName(label: String): String = {
"label-" + label
}
}
Procedure in Neo4j always return result in Stream and it is a latest feature in Java8 so we will also used Java Class for return the final result and For defining the public variable.
We will create Java class for result :
public class JavaHelper {
#Context
public GraphDatabaseService db;
#Context
public Log log;
public static class SearchHit {
//your result code here
}
You can refer knoldus blog for Neo4j User Defined Procedure for creating and storing Neo4j Procedure with Scala. Here you will also find sample code with git hub repository.
I'd like to know how to create a method that will allow me to generically do this...
public class Repo<T> : IGenericRepo<T> where T : class
{
protected PteDotNetEntities db;
public T Get(int id)
{
//how do I dynamically get to the correct entity object and select it by
//id?
}
}
Yes you can. If you know that all your entities will have simple primary key property of type int and name Id you can do simply this:
public interface IEntity
{
int Id { get; }
}
All your entities must implement this interface. Next you can simply do:
public class Repo<T> : IGenericRepo<T> where T : class, IEntity
{
protected PteDotNetEntities db;
public T Get(int id)
{
return db.CreateObjectSet<T>().FirstOrDefault(e => e.Id == id);
}
}
This is the simplest possible solution. There are better solutions using GetObjectByKey but they are more complex. The difference between FirstOrDefault and GetObjectByKey is repeatable execution. FirstOrDefault always executes DB query whereas GetObjectByKey first checks if the entity with the same key was already loaded / attached to the context and returns it without querying the database. As reference for version using GetObjectByKey you can check similar questions:
Entity Framework Simple Generic GetByID but has differents PK Name
Generic GetById for complex PK
You can simplify those examples if you know the name of the key property upfront (forced by the interface).
In case of using code first / DbContext API you can also check this question:
Generic repository EF4 CTP5 getById