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Hello,

I work on a db4o database, which should store parameters from different devices. My actually structure is like this:

public class Parameter {
    public boolean write,...;
    public int nr, access, hash ...;
    public VaildValues vaildValues;
    public VaildEnum vaildEnum;
   
    public Parameter(int nr, boolean write, int access) {
        this.nr = nr;
        this.access = access;
        this.write = write;
    }

There are a lot more fields in that class. The fields VaildValues and VaildEnum are optional.

public class Device {
    public int firmware;
    public String type;
    public List parameter;
    public Device(int firmware, String type)
    {
        this.firmware = firmware;
        this.type = type;
        parameter = new ArrayList();
    }
}

That's the class, which hold the parameter for the different devices.

My first problem is, that more devices could have the same parameter and I don't want to store the same parameter twice in the database. So I look for each parameter if it is already in the database befor putting it there:

    Query query = db.query();
            query.constrain(Parameter.class);
            query.descend("nr").constrain(p.nr);
            query.descend("hash").constrain(p.hash);
            ObjectSet result = query.execute();
           
           
            if (result.size() > 0) {
                device.parameter.add(result.get(0));           
            }
            else
                device.parameter.add(p);

The hash is a field, there I hash over all elements in the Parameter.class, so that I only have to compare the parameter number and the hash value. To make things a little bit faster, I indexed the nr and index value. But to insert 1000 parameter, which are already in the database i need over 30 seconds.

Another problem is that every parameter have a label in english and german. But I don' t have a idea how to store that in a efficent way in relation to a parameter. I don't want to store it in a field in the parameter class. Because it could be that parameter that aren't exactly the same have the same label. So also here I don't want to store them twice in the database.

Before I work with dbo4 I stored the parameter in a SQLite database. There was an option, that I could define  fields as "unique on confilct ignore" and if I add a parameter which is already in the database I got back the existing index of the parameter. That method was extrem fast and stable. Is there any function like that in db4o?

Thank you for your answer! I tried that, but there are two problems with unique fields:

My first Problem is that I could have the same Parameternumber with different options. So I could not define the parameter number as unique. I must store several fields in one unique contraint. In SQLite I done that like that "UNIQUE (paramnr, write, access, ...) ON CONFLICT IGNORE" so that only if all fields are the same I got an on conflict error.

Another problem is, that I have to commit each time then I store a parameter. But if I add more than 2000 parameter, this makes things extremly slow. The problem is, that more than 90% of the parameter are exactly the same. And each time, if the parameter is already in the database I have to search for the reference.

Yesterday I found a solution, that works in 10s, but I don't think, that it is like "best practice":

     
        allParams = new ArrayList();
        for (Parameter p : db.query(Parameter.class)) {
            allParams.add(p);
        }           

Befor I add a new device with several parameter to the database, I store all parameter existing in the database in an Arraylist. Than I look for each parameter with allParams.indexOf(newParam) if it's already there. I don't think that this is a good way to do that. But if I always query over the database I need over a minute. I think that there aren't all information in the memory. Is there a way to do this without an ArrayList in the same speed?

Thanks & regards

Christopher