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Difference between revisions of "EDT:Working with a database"
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* -- ID indicates that the field and its value are set to equal | * -- ID indicates that the field and its value are set to equal | ||
* in the default SQL INSERT statement (for an EGL add statement) and | * in the default SQL INSERT statement (for an EGL add statement) and | ||
− | * in the default SELECT | + | * in the default SELECT statement (for an EGL get or open statement). |
*/ | */ | ||
Revision as of 18:21, 10 February 2012
Much of the code on this page accesses a database table that is defined here:
CREATE TABLE PAYMENT ( PAYMENT_ID INT PRIMARY KEY NOT NULL GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1), CATEGORY INT, DESCRIPTION CHAR(30), AMOUNT DECIMAL(10,2), FIXED_PAYMENT SMALLINT, DUE_DATE DATE, PAYEE_NAME CHAR(30), PAYEE_ADDRESS1 CHAR(30), PAYEE_ADDRESS2 CHAR(30) );
Contents
Following the typical pattern
Here is the typical pattern for interacting with a relational database:
- Define a Record, Handler, or external type and include annotations. For a Record type, you might use a Workbench capability to retrieve details from a database management system.
- Declare a variable that is based on the defined type. Your code will copy data between the database and that variable.
- Declare variables to represent the SQL data sources. Each data source is a connection or a result set.
- Configure EGL statements that reference variables that you declared. For each statement, rely on the SQL code that is provided for you or customize that code.
Defining a Record type
/* * The annotations help to define the default SQL code when * a record of this type is used in a given EGL statement: * -- Table refers to the table being accessed. If Table is not supplied, * the name of the Record type is assumed to be the table name. * -- Column refers to the column being accessed. If Column is not supplied, * the name of the field is assumed to be the name of the column. * -- ID indicates that the field and its value are set to equal * in the default SQL INSERT statement (for an EGL add statement) and * in the default SELECT statement (for an EGL get or open statement). */ Record PaymentRec { @Table {name="PAYMENT"} } paymentId int {@ID, @GeneratedValue, @Column { name="PAYMENT_ID" } }; category int { @Column { name="CATEGORY" } } ; description string? { @Column { name="DESCRIPTION" } } ; amount decimal(10,2) { @Column { name="AMOUNT" } } ; fixedPayment boolean { @Column { name="FIXED_PAYMENT" } } ; dueDate date { @Column { name="DUE_DATE" } } ; payeeName string { @Column { name="PAYEE_NAME" } } ; payeeAddress1 string { @Column { name="PAYEE_ADDRESS1" } } ; payeeAddress2 string { @Column { name="PAYEE_ADDRESS2" } } ; End
Getting a row
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
Getting multiple rows with one EGL statement
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
Adding a row
function addCustomer{customer Customer in} ds SQLDataSource?{@resource {}}; add customer to ds; end
Looping through an 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
For More Information
For details on how to connect to a database, see SQL database bindings.
For a keystroke-by-keystroke tutorial, see Access a database with EGL Rich UI. The third lesson shows how to define a Record type to match details that are stored in a database management system.