Versant Object Database Aggregation Query
Versant Object Database is a Object database, which is mainly used to store and manage object data. As it is an object-oriented database, it stores data not through tables or rows, but through objects.
Therefore, Versant Object Database does not directly support traditional SQL aggregation queries such as SUM, COUNT, MIN, MAX, and AVG. However, it provides some other ways to implement aggregation related operations. Here are some examples:
1. Traverse and Accumulate: Aggregation is achieved by traversing a collection of objects and gradually accumulating object attribute values. For example, if there is a collection of Person objects, each with an age attribute (age), the following code can be used to calculate the total age of everyone:
int totalAge = 0;
for (Person person : personCollection) {
totalAge += person.getAge();
}
System.out.println("Total age: " + totalAge);
2. Filtering and counting: Use criteria to filter objects, and then calculate the number of filtered objects. For example, if there is a collection of Car objects, each with a color attribute (color), the following code can be used to calculate the number of cars with a red color:
int redCarCount = 0;
for (Car car : carCollection) {
if (car.getColor().equals("red")) {
redCarCount++;
}
}
System.out.println("Red car count: " + redCarCount);
3. Attribute statistics: Implement attribute statistics by traversing the object collection and recording the values of attributes. For example, if there is a collection of Product objects, each with a price attribute (price), the following code can be used to calculate the minimum and maximum prices of all products:
double minPrice = Double.MAX_VALUE;
double maxPrice = Double.MIN_VALUE;
for (Product product : productCollection) {
double price = product.getPrice();
if (price < minPrice) {
minPrice = price;
}
if (price > maxPrice) {
maxPrice = price;
}
}
System.out.println("Min price: " + minPrice);
System.out.println("Max price: " + maxPrice);
It should be noted that these examples only demonstrate using Java code to implement operations similar to aggregate queries. In Versant Object Database, these operations can be further expanded and optimized based on specific requirements and business logic, and more complex query and statistical functions can be achieved by combining with other characteristics of the database.
