code: public boolean delete(String tableName, String primaryKey, Record record) {
  		String[] pKeys = primaryKey.split(",");
  		if (pKeys.length <= 1) {
  			Object t = record.get(primaryKey);	// 引入中间变量避免 JDK 8 传参有误
  			return deleteByIds(tableName, primaryKey, t);
  		}
  		
  		config.dialect.trimPrimaryKeys(pKeys);
  		Object[] idValue = new Object[pKeys.length];
  		for (int i=0; i<pKeys.length; i++) {
  			idValue[i] = record.get(pKeys[i]);
  			if (idValue[i] == null)
  				throw new IllegalArgumentException("The value of primary key \"" + pKeys[i] + "\" can not be null in record object");
  		}
  		return deleteByIds(tableName, primaryKey, idValue);
  	}
docs: Delete record.
  <pre>
  Example:
  boolean succeed = Db.use().delete("user", "id", user);
  </pre>
  @param tableName the table name of the table
  @param primaryKey the primary key of the table, composite primary key is separated by comma character: ","
  @param record the record
  @return true if delete succeed otherwise false