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Difference between revisions of "EDT:Working with a database"
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STATE string?; // nullable field | STATE string?; // nullable field | ||
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= '''Getting a record''' = | = '''Getting a record''' = |
Revision as of 15:28, 10 February 2012
Here is the typical pattern for interacting with a relational database:
- Define a Record, Handler, or external type and include annotations.
- Declare a variable that is based on the defined types. Your code will copy data between the database and the memory area that is named by the variable.
- Declare variables to represent SQL data sources, each of which is connection detail or a result set.
- Configure EGL statements that reference the declared variables. For each statement, rely on the SQL code that is provided by default or customize the code.
Defining a record
record CUSTOMER type Entity{@table{name = "CUSTOMER"}} // record is bound to the CUSTOMER table (or view) CUSTID string{@id}; // primary key field NAME string; COUNTRY string; STATE string?; // nullable field end
Getting a record
function getCustomer(someId String in} returns (Customer) ds SQLDataSource?{@resource {}}; // declares a data source that will use binding name "ds" (since a name is not specified) aCust Customer; // declares and empty customer record get aCust from ds using(someId); // gets the record in the table that has a key value of someID and populates the customer record get aCust from ds using(someId) with #sql{ // alternative approach for getting a single record (allows for customizing the SQL) SELECT * FROM CUSTOMER WHERE id = ? }; vals Dictionary; // declares a new dictionary get vals from ds using(someId) with #sql{ // alternative approach for getting a single record (does not require a Record definition) SELECT * FROM CUSTOMER WHERE id = ? }; // creates a key/value pair in the dictionary for each column in the result set return (aCust); end
function getCustomer(} returns (Customer[]) ds SQLDataSource?{@resource {}}; // declares a data source that will use binding name "ds" (since a name is not specified) custs Customer[]; // declares a new dynamic array of customer records get custs from ds; // populates the array with a Customer record for each row in the result set get custs from ds with #sql { select * from customer where state = 'CO' }; // populates the array, but with a limited set of Customer records state String = "CO"; get custs from ds using(state) with #sql { select * from customer where state = ? }; // parameterized version of the previous example end
Inserting a record
function addCustomer{customer Customer in} ds SQLDataSource?{@resource {}}; add customer to ds; end
Looping through a SQL result set
function loopCust() ds SQLDataSource?{@resource{uri = "binding:myDB" }}; // declares a new data source rs SQLResultSet?; // declares a new result set open rs from ds with #sql{ // opens a result set using the specified SQL query SELECT * FROM CUSTOMER }; myCust Customer; //Loop through results and write out customer name while(rs.getNext()) get myCust from rs; Syslib.writeStdOut ("Customer name: " + myCust.name); end end