CODEWITHSUNDEEP
javamysqlsqlhibernatehibernate-criteria
user3708842
user3708842

Reputation: 563

Join using Hibernate Criteria without using Alias on Restriction

I have an object with 70 attributes. For ease of use I created 2 objects, a 'main' object and a 'details' object, with 1:1 relationship based on an auto-generated integer ID. I had a SEARCH screen that allowed searching on any of the main attributes, for which I build Restriction objects for whatever the user typed in. What was nice was that I did this all through iterating through the fields and building criterion - I didn't need ugly code to specifically handle each of the 30 attributes.

Now they want to search on the details fields as well. My previous screen-field-iterating code works perfectly with no changes (the whole reason for making it 'generic'), however I cannot get the JOIN to work to query on details fields.

class House {
    Integer houseID;
    String address;
    . . .
    HouseDetails houseDetails;
}

class HouseDetails {
    Integer houseID;
    String color;
    . . .
}

I tried to create an alias and add it to the criteria :

criteria.createAlias("houseDetails", "houseDetails");

but I get this error :

org.hibernate.QueryException: could not resolve property: color of: House

Here's the thing - I know this would work if I prefix my restrictions with the alias name, but I do NOT want to have to know which table (House or HouseDetails) the field comes from. That would ruin all the automatic looping code and create specific code for each field.

Since SQL can do this as long as the column names are unique :

select * from house, housedetails where house.houseID = housedetails.houseID 
and color = 'blue';

I'm wondering how can I get this to work using criteria??

As an aside, but related to this : Is there a way to perform something like Java's introspection on Hibernate HBM.XML mapping files? A number of times I've wanted to do this to solve problems but never found an answer. For the above problem, if I could easily find out which table contained each field, I could add the prefix to the Restriction. Something like this :

// Map of search keys (columns) to searching values
for ( String key : parms.keySet() ) {
    String val = parms.get(key);

    if ( HIBERNATE-SAYS-KEY-IS-FROM-DETAILS-TABLE ) {
        key = "houseDetails." + key;            
    }    
    criteria.add(Restrictions.eq(key,val));
}

Upvotes: 1

Views: 3633

Answers (2)

nuno
nuno

Reputation: 1791

The alias mechanism in hibernate and the Criteria API is pretty well specified. I suggest going through the documentation a little a bit.

I think what you want is something like this:

Criteria criteria = session.createCriteria(House.class);
criteria.createAlias("houseDetails.color", "houseColor");
criteria.add(Restrictions.eq("houseColor", "red"));

Upvotes: 1

Amogh
Amogh

Reputation: 4573

You can make method to find table name for passed column name.

By using SessionFactory.getClassMetaData() you can get all the information about that class. Once you have ClassMetaData then you can get all the property names. An demo method is shown below:

public String findTableName(String columnName)
{
    boolean found=false;
    Map<String, ClassMetadata> classMetaData =  sessionFactory.getAllClassMetadata();
    for (Entry<String, ClassMetadata> metaData : classMetaData.entrySet()) 
    {
        String[] propertyNames = metaData.getValue().getPropertyNames();                    
        for (String property : propertyNames) 
        {           
            if(property == columnName)
            {
                return metaData.getKey() + "." + property;    
                found=true;
                break;
            }
        }
        if(found)
            break;
    }       
}

Upvotes: 1

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