Examples of tokyocabinet.BDBCUR

tokyocabinet.BDBCUR
Cursor is a mechanism to access each record of B+ tree database in ascending or descending order.


    private BDBCUR cursor;
    private boolean firstNextCall;


    public TokyoDataStoreIterator(BDB bdb) {
        this.cursor = new BDBCUR(bdb);
        // flag to indicate this is the first call to next()
        this.firstNextCall = true;
    }

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  public void push_back(String key, byte[] value) throws TException {
    
    //first get the next key.
    List<byte[]> nextKey = bdb.fwmkeys(key.getBytes(),2);
    
    BDBCUR cursor = new BDBCUR(bdb);
    
    //look for edge cases
    
    //no forward keys
    if(nextKey.isEmpty() ){
      this.put(key, value);
      return;
    }
        
    //the input is all that was found. jump to last record.
    if( Arrays.equals(nextKey.get(0),key.getBytes()) && nextKey.size() == 1){
      if(!cursor.last())
        throw new RuntimeException("Can't jump to last record");
    }else{
    
      //jump to key ahead of our input key
      if(nextKey.size() == 1){    
        if(!cursor.jump(nextKey.get(0)))
          throw new RuntimeException("Key should exist but failed to jump to it's location");        
      } else {
        if(!cursor.jump(nextKey.get(1)))
          throw new RuntimeException("Key should exist but failed to jump to it's location");
      }    
    }
    
    //back one should be the input key, if it's not then the key 
    //does not exist yet, so we add it
    if(!Arrays.equals(cursor.key(),key.getBytes())){
      if(!cursor.prev()){
        this.put(key, value);
        return;
      }
    }
    
    // the key under this cursor should match, if not we add a new key
    //based on input
    if(!Arrays.equals(cursor.key(),key.getBytes())){
      this.put(key, value);
      return;
    }
    
    //we are at the right spot, now append the value
    if(!cursor.put(value, BDBCUR.CPAFTER))    
      throw new TException(bdb.errmsg());
      
  }

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  public byte[] pop_back(String key) throws TException{
    
    //first get the next key.
    List<byte[]> nextKey = bdb.fwmkeys(key.getBytes(),2);
    
    BDBCUR cursor = new BDBCUR(bdb);
    
    if(nextKey.isEmpty()){
      return new byte[]{};    
    }
    
    //first entry should match, if not the input key is missing so fail
    if(!Arrays.equals(nextKey.get(0),key.getBytes())){
      
      return new byte[]{};
    
    }
    
    //the input key is at the end of the index so jump to end
    if(nextKey.size() == 1) {
      
      if(!cursor.last())
        throw new RuntimeException("Unable to jump to last key");
      
    } else {
      
      if(!cursor.jump(nextKey.get(1)))
        throw new RuntimeException("Key should exist but failed to jump to it's location");
      
    }
    
      
    //move back one, to tail of the input key
    if(!cursor.prev())
      throw new RuntimeException("Key should exist but failed to jump to it's location");
    
    if(!Arrays.equals(cursor.key(),key.getBytes()))
      throw new TException("key mismatch "+key+" vs "+cursor.key2());
  
    byte[] value = cursor.val();
    
    //delete
    if(!cursor.out())
      throw new TException(bdb.errmsg());
    
    
    return value;
  }

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    return value;
  }
  
  public void push_front(String key, byte[] value) throws TException {


    BDBCUR cursor = new BDBCUR(bdb);
    
    if(!cursor.jump(key)){
      this.put(key, value);
      return;
    }
    
    //not matching key so add new
    if(!Arrays.equals(cursor.key(),key.getBytes())){
      this.put(key, value);
      return;
    }
    
    if(!cursor.put(value, BDBCUR.CPBEFORE))
      throw new TException(bdb.errmsg());
    
  }

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  }
  
  public byte[] pop_front(String key) throws TException{
    
    BDBCUR cursor = new BDBCUR(bdb);
    
    if(!cursor.jump(key))
      return new byte[]{};
    
    if(!Arrays.equals(cursor.key(),key.getBytes()))
      return new byte[]{};
  
    
    //save value
    byte[] value = cursor.val();
      
    
    //delete
    if(!cursor.out())
      throw new TException(bdb.errmsg());
    
    return value;
  }

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  private BDBCUR goto_position(String key, int position) {
    if(position < 0)
      return null;
    
    BDBCUR cursor = new BDBCUR(bdb);
    
    if(!cursor.jump(key))
      return null;
    
    int currentPos = 0;
    int checkMod = 10; //verify key every few records
    while(currentPos < position){
      cursor.next();
      
      if(currentPos % checkMod == 0){
        
        if(!Arrays.equals(cursor.key(), key.getBytes()))
          return null;
        
      }
      
      currentPos++;
    }
    
    //at position
    if(!Arrays.equals(cursor.key(), key.getBytes()))
      return null;
    
    
    return cursor;
  }

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    return cursor;
  }
  
  public byte[] remove_at(String key, int position){
    
    BDBCUR cursor = this.goto_position(key, position);
    
    //if position not found
    if(cursor == null)
      return null;
    
    byte[] value = cursor.val();
    
    if(!cursor.out())
      throw new RuntimeException("Unable to remove record");
  
    return value;
  }

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    return value;
  }
  
  public void insert_at(String key, byte[] value, int position) {
    BDBCUR cursor = this.goto_position(key, position);
    
    if(cursor == null)
      throw new RuntimeException("Unable to insert at position: "+position);
    
    if(!cursor.put(value, BDBCUR.CPBEFORE))
      throw new RuntimeException("Unable to replace record");
  }

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    if(!cursor.put(value, BDBCUR.CPBEFORE))
      throw new RuntimeException("Unable to replace record");
  }
  
  public void replace_at(String key, byte[] value, int position) {
    BDBCUR cursor = this.goto_position(key, position);
    
    if(cursor == null)
      return;
    
    if(!cursor.put(value, BDBCUR.CPCURRENT))
      throw new RuntimeException("Unable to replace record");
  }

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    if(!cursor.put(value, BDBCUR.CPCURRENT))
      throw new RuntimeException("Unable to replace record");
  }
  
  public byte[] retrieve_at(String key, int position){
    BDBCUR cursor = this.goto_position(key, position);
    
    //if position not found
    if(cursor == null)
      return null;
    
    byte[] value = cursor.val();
    
  
    return value;
  }

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Related Classes of tokyocabinet.BDBCUR

com.cloudhopper.datastore.tokyo.TokyoDataStoreIterator

org.thrudb.thrudoc.tokyocabinet.TokyoCabinetDB

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