How u guys build query in program

Question

Hey guys,
i was wondering how u guys build queries in the program. i mean if you use String or StringBuffer. e.g.
SELECT * FROM MY_TABLE WHERE X=someValue and Y=someValue and Z= someValue. if i use String i have to use + operator to get the values at runtime and which causes problem with performence. and when i use StringBuffer its kind of cumbersome. whats the best way you guys find for building queries at run time.
appreciate the time you have taken to read this.
take care and have a good day.

Answer 1

Hi
yes i'm creating the query in a loop. query is very
big like 2 page long. basically i've to join data from
many tables and many filter criteria entered by the
clients which i put in the where clause. we r running
optimizers on our application and it shows query
building processes are making the overall performence
slow.
First you limit the query in some fashion (if you don' t then you might as well just give them a text box and let them type SQL.)
In your case that might be limiting it to a query on all of the five tables.
Second you produce a query DTO.
A standard DTO might look like this....
       class CustomerDTO
         public String customerName;
         public double accountBalance;
  A query DTO, built to match the above, would look like this....
       class CustomerQueryDTO
         public String customerName1;
         public String customerName2;
         public OperatorType customerNameOperator;
        public double accountBalance1;
        public double accountBalance2;
        public OperatorType accountBalanceOperator;
      }And OperatorType would allow equality, between (which is why there are two parameters), greater than, etc
You build the query string as follows
       CustomerQueryDTO query = ...
       StringBuffer b = new StringBuffer();
       b.append("select ");
       b.append(fieldList);
       b.append(" from ");
       b.append(tableList);
       b.append("where 1=1");
       if (query.customerNameOperator != null)
            b.append(" and ");
            String exp = createExpression(query.customerName1,
                                   query.customerName2,
                                   query.customerNameOperator );
            b.append(exp);
     String sql = b.toString(); 
You also want to make sure that a query actually is limited by something. So the query must have at least one clause.