How to use join query for displaying data from multiple tables in greenDAO?

问题

Following is my DAOgenerator class:

public class MyDaoGenerator {

    public static void main(String args[]) throws Exception {
        Schema schema = new Schema(3, "Dao");

        Entity employee = schema.addEntity("Employee");
        employee.addIdProperty().autoincrement();
        employee.addStringProperty("name");
        employee.addStringProperty("mobile");
        employee.addStringProperty("address");
        employee.addStringProperty("company_id");

        Entity company = schema.addEntity("Company");
        company.addIdProperty().autoincrement();
        company.addStringProperty("comp_name");
        company.addStringProperty("comp_location");
        company.addStringProperty("comp_address");



        new DaoGenerator().generateAll(schema, args[0]);
    }
}

Following is my DAO queries class. This class has all the function like insert, delete, clear table:

public class DaoQueries {

    private static CompanyDao getMyCompanyDao(Context context){
        return ((AppMain)context.getApplicationContext()).getDaoSession().getCompanyDao();
    }


    public static void AddCompany(Context context,Company company){
        getMyCompanyDao(context).insertOrReplace(company);
    }

    public static int companySize(Context context){
        return  getMyCompanyDao(context).loadAll().size();
    }    

    public static List<Company> getCompanies(Context context){
        return getMyCompanyDao(context).loadAll();
    }

    private static EmployeeDao getEmployeeDao(Context context){
        return ((AppMain)context.getApplicationContext()).getDaoSession().getEmployeeDao();
    }
    public static void AddEmployee(Context context,Employee employee){
        getEmployeeDao(context).insertOrReplace(employee);
    }    


    public static List<Employee> getEmployees(Context context){
        return getEmployeeDao(context).loadAll();
    }

    public static void joinedUser(Context context){

        QueryBuilder<Employee> queryBuilder = getEmployeeDao(context).queryBuilder();
        queryBuilder.join(Company.class,CompanyDao.Properties.Id)
            .where(CompanyDao.Properties.Id.eq(1));

        List<Employee> employees = queryBuilder.list();
        Log.e("DAO","EMPLOYE JOIN "+employees.size());

    }
}

I tried join query with greenDAO as mentioned in dao documentation for getting rows from both the tables like this:

public static void joinedUser(Context context){

    QueryBuilder<Employee> queryBuilder = getEmployeeDao(context).queryBuilder();
    queryBuilder.join(Company.class,CompanyDao.Properties.Id)
            .where(CompanyDao.Properties.Id.eq(1));

    List<Employee> employees = queryBuilder.list();
    Log.e("DAO","EMPLOYE JOIN "+employees.size());

}

回答1:

If you want to show data from both tables, you can use greenDAO relations. In your case, you will need a 1:1 relation between Employee and Company. So, greenDAO will create a Employee class with a member of type Company and when you load a Employee, greenDAO will perform the join query and load the related company.

The new generator code:

public class MyDaoGenerator {

    public static void main(String args[]) throws Exception {
        Schema schema = new Schema(3, "Dao");
        Entity company = schema.addEntity("Company");
        company.addIdProperty().autoincrement().notNull();
        company.addStringProperty("comp_name");
        company.addStringProperty("comp_location");
        company.addStringProperty("comp_address");


        Entity employee = schema.addEntity("Employee");
        employee.addIdProperty().autoincrement();
        employee.addStringProperty("name");
        employee.addStringProperty("mobile");
        employee.addStringProperty("address");
        Property companyId = employee.addLongProperty("company_id").getProperty();
        employee.addToOne(company, companyId);

        new DaoGenerator().generateAll(schema, args[0]);
    }

}

Getting the employees of company with company_id = 1:

QueryBuilder<Employee> queryBuilder = getEmployeeDao(context).queryBuilder();
List<Employee> employees = qb.where(EmployeeDao.Properties.Company_id.eq(1)).list();

Iterating through employees:

foreach(Employee employee : employees){
    Company company = employee.getCompany();
    String companyAddress = company.getComp_address(); 
    //...
}

For more info, check greeenDAO Relations Docs.

来源：https://stackoverflow.com/questions/38315642/how-to-use-join-query-for-displaying-data-from-multiple-tables-in-greendao

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android

greendao