CODEWITHSUNDEEP
java
user1920811
user1920811

Reputation:

Add multiple key value pairs from a database table to a HashMap

I have three database tables defined below, column names mentioned in parenthesis:

Product (ProductID, Price, Last_Updated)

User (UserID, Name, Address, LocationID, Last_Updated)

Location (LocationID, Loc_Name, Last_Updated)

I want to use Java (JDK 1.5) to add all the column names of all the tables in one collection like a HashMap.

My problem is when a duplicate key is entered, the previous value is over ridden.

I am adding them like:

Map<String, String> map = new HashMap<String, String>();

map.add("ProductID", "Save the Product ID");
// ...
map.add("Last_Updated", "Save Last_Updated of Product table");
// ...
map.add("LocationID", "Save the LocationID");
// ...
map.add("Last_Updated", "Save Last_Updated of User table.");

Now the key Last_Updated is overridden with new value Save Last_Updated of User table.

But I want both the values.

Is there any way to implement this without using multiple HashMap structures?

Upvotes: 0

Views: 6611

Answers (5)

Bal&#225;zs &#201;des
Bal&#225;zs &#201;des

Reputation: 13807

If you want to add items with the same key, then this would be a possible solution

Map<String, List<String>> map = new HashMap<String, List<String>>();

when adding an element:

public void add(String key, String value) {
    if(!map.containsKey(key)) {
        map.put(key, new ArrayList<String>());
    }
    map.get(key).add(value);
}

And when you want to access an element, then by the maps get() function you will get a List of strings, wich are the values for a key.

However, it would be best to use a Multimap implementation:

Guava:

Multimap - You can see the concrete implementations in the javadoc.

Multimap<String, String> map = ArrayListMultimap.create();
map.put("a", "Apple");
map.put("a", "Almonds");
Collection<String> valuesForA = map.get("a"); // List of ("Apple", "Almonds")

Apache Commons

MultiMap - Examples and concrete implementations in the javadoc

Upvotes: 2

user1920811
user1920811

Reputation:

Use Seperator. Like Pipe symbol (|) or Dot (.)

Upvotes: 0

Urs Reupke
Urs Reupke

Reputation: 6921

If you are limited to JDK 5, but allowed to use libraries, check out a publicly available MultiMaps: Guava has one, as does Commons Collections

Upvotes: 1

Aravind Yarram
Aravind Yarram

Reputation: 80176

Why not a denormalized table in an in-memory db like H2 or HSQL etc.

Upvotes: 0

S.L. Barth is on codidact.com
S.L. Barth is on codidact.com

Reputation: 8245

Add the table names as a prefix to your column names. Then you can separate "Product.Last_Updated", "User.Last_Updated" and "Location.Last_Updated".
Obviously you have to use a separator char that is not used in the names of your tables or columns; a '.' should do.

Upvotes: 1

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