$Id: db-api.txt,v 1.7 2003/09/15 22:34:28 janakj Exp $

Generic Database Interface
--------------------------

This is a generic database interface for modules that need to utilize a 
database. The interface should be used by all modules that access database.
The interface will be independent of the underlying database server.

Notes:

If possible, use predefined macros if you need to access any structure 
attributes.  

For additional description, see comments in sources of mysql module.

If you want to see more complicated examples of how the API could be used, 
see sources of dbexample, usrloc or auth modules.


1 Data types

There are several new data types. All of them are defined in header file db.h,
a client must include the header file to be able to use them.

1.1 Type db_con_t

1.1.1 Description

This type represents a database connection, all database functions (described 
below) use a variable of this type as one argument. In other words, variable 
of db_con_t type serves as a handle for a particular database connection.

1.1.2 Definition

   typedef struct db_con {
        char* table;     /* Default table to use */
        void* con;       /* Database connection */
        void* res;       /* Result of previous operation */
        void* row;       /* Internal, not for public use */
        int connected;   /* 1 if connection is established */
   } db_con_t;

1.1.3 Macros

There are no macros for db_con_t type.


1.2 Type db_key_t

1.2.1 Description

This type represents a database key. Every time you need to specify a key 
value, this type should be used. In fact, this type is identical to const 
char*.

1.2.2 Definition
   
   typedef const char* db_key_t;

1.2.3 Macros

There are no macros (It is not needed).


1.3 Type db_type_t

1.3.1 Description

Each cell in a database table can be of a different type. To distinguish
among these types, the db_type_t enumeration is used. Every value of the
enumeration represents one datatype that is recognized by the database
API. This enumeration is used in conjunction with db_type_t. For more
information, see the next section.

1.3.2 Definition

   typedef enum {
       DB_INT,       /* Integer number */
       DB_DOUBLE,    /* Decimal number */
       DB_STRING,    /* String */
       DB_STR,       /* str structure */
       DB_DATETIME   /* Date and time */
       DB_BLOB       /* Binary large object */
       DB_BITMAP     /* Bitmap, one-dimensional array of flags */
   } db_type_t;

1.3.3 Macros

There are no macros.


1.4 Type db_val_t

1.4.1 Description

This structure represents a value in the database. Several datatypes are
recognized and converted by the database API:

DB_INT      - Value in the database represents an integer number
DB_DOUBLE   - Value in the database represents a decimal number
DB_STRING   - Value in the database represents a string
DB_STR      - Value in the database represents a string
DB_DATETIME - Value in the database represents date and time
DB_BLOB     - Value in the database represents binary large object
DB_BITMAP   - Value in the database represents an array of flags

These datatypes are automaticaly recognized, converted from internal database
representation and stored in the variable of corresponding type.

1.4.2 Definition

    typedef struct db_val {
         db_type_t type;              /* Type of the value */
         int nul;                     /* NULL flag */
         union {                      
             int int_val;             /* Integer value */
             double double_val;       /* Double value */
             time_t time_val;         /* Unix time_t value */
             const char* string_val;  /* Zero terminated string */
	     str str_val;             /* str structure */
             str blob_val;            /* Structure describing blob */
             unsigned int bitmap_val; /* Array of flags */
         } val;
    } db_val_t;

1.4.3 Macros

Note: All macros expect reference to db_val_t variable as the parameter.

1.4.3.1 VAL_TYPE(value) Macro

Use this macro if you need to set/get the type of the value

Example: VAL_TYPE(val) = DB_INT;
         if (VAL_TYPE(val) == DB_FLOAT) ...

1.4.3.2 VAL_NULL(value) Macro

Use this macro if you need to set/get the null flag. Non-zero flag means that 
the corresponding cell in the database contained no data (NULL value in MySQL
terminology).

Example: if (VAL_NULL(val) == 1) {
             printf("The cell is NULL");
         }

1.4.3.3 VAL_INT(value) Macro

Use this macro if you need to access integer value in the db_val_t structure.

Example: if (VAL_TYPE(val) == DB_INT) {
             printf("%d", VAL_INT(val));
         }

1.4.3.4 VAL_DOUBLE(value) Macro 

Use this macro if you need to access double value in the db_val_t structure.

Example: if (VAL_TYPE(val) == DB_DOUBLE) {
             printf("%f", VAL_DOUBLE(val));
         }

1.4.3.5 VAL_TIME(value) Macro 

Use this macro if you need to access time_t value in the db_val_t structure.

Example: time_t tim;
         if (VAL_TYPE(val) == DB_DATETIME) {
             tim = VAL_TIME(val);
         }

1.4.3.6 VAL_STRING(value) Macro 

Use this macro if you need to access string value in the db_val_t structure.

Example: if (VAL_TYPE(val) == DB_STRING) {
             printf("%s", VAL_STRING(val));
         }

1.4.3.7 VAL_STR(value) Macro

Use this macro if you need to access str structure in the db_val_t structure.

Example: if (VAL_TYPE(val) == DB_STR) {
             printf("%.*s", VAL_STR(val).len, VAL_STR(val).s);
         }

1.4.3.8 VAL_BLOB(value) Macro

Use this macro if you need to access blob value in the db_val_t structure.

Example: if (VAL_TYPE(val) == DB_BLOB) {
	     printf("%.*s", VAL_BLOB(val).len, VAL_BLOB(val).s);
         }

1.4.3.9 VAL_BITMAP(value) Macro

Use this macro if you need to access bitmap value in the db_val_t structure.

Example: if (VAL_TYPE(val) == DB_BITMAP) {
	    printf("%d", VAL_BITMAP(val));
	 }

1.5 Type db_row_t

1.5.1 Description

This type represents one row in a database table. In other words, the row is an
array of db_val_t variables, where each db_val_t variable represents exactly 
one cell in the table.

1.5.2 Definition

   typedef struct db_row {
       db_val_t* values;    /* Array of values in the row */
       int n;               /* Number of values in the row */
   } db_val_t;

1.5.3 Macros

1.5.3.1 ROW_VALUES(row) Macro 

Use this macro to get pointer to the array of db_val_t structures.

Example: db_val_t* v = ROW_VALUES(row);
         if (VAL_TYPE(v) == DB_INT) ....

1.5.3.2 ROW_N(row) Macro 

Use this macro to get number of cells in the row.

Example: db_val_t* val = ROW_VALUES(row);
         for(i = 0; i < ROW_N(row); i++) {
             switch(VAL_TYPE(val + i)) {
             case DB_INT: ...; break;
             case DB_DOUBLE: ...; break;
             ...
             }
         }


1.6 Type db_res_t

1.6.1 Description

This type represents a result returned by db_query function (see below). The 
result can consist of zero or more rows (see db_row_t description).

Note: A variable of type db_res_t returned by db_query function uses dynamicaly
      allocated memory, don't forget to call db_free_query if you don't need 
      the variable anymore. You will encounter memory leaks if you fail to do 
      this !

In addition to zero or more rows, each db_res_t object contains also an array 
of db_key_t objects. The objects represent keys (names of columns).

1.6.2 Definition

   typedef struct db_res {
       struct {
           db_key_t* keys;    /* Array of column names */
           db_type_t* types;  /* Array of column types */
           int n;             /* Number of columns */
       } col;
       struct db_row* rows;   /* Array of rows */
       int n;                 /* Number of rows */
   } db_res_t;

1.6.3 Macros

1.6.3.1 RES_NAMES(res) Macro 

Use this macro if you want to obtain pointer to the array of cell names.

Example: db_key_t* column_names = ROW_NAMES(row);

1.6.3.2 RES_COL_N(res) Macro 

Use this macro if you want to get the number of columns in the result.

Example: int ncol = RES_COL_N(res)
         for(i = 0; i < ncol; i++) {
             /* do something with the column */
         }

1.6.3.3 RES_ROWS(res) Macro 

Use this macro if you need to obtain pointer to array of rows.

Example: db_row_t* rows = RES_ROWS(res);
 
1.6.3.4 RES_ROW_N(res) Macro 

Use this macro if you need to obtain the number of rows in the result

Example: int n = RES_ROW_N(res);


1.7 Type db_op_t

1.7.1 Description

This type represents an expression operator. In fact, this type is 
identical to const char*.

1.7.2 Definition
   
   typedef const char* db_op_t;

1.7.3 Macros

There are no macros (It is not needed).


2 Functions

There are several functions that implement the database API logic. All function
names start with db_ prefix, except bind_dbmod. bind_dbmod function is 
implemented in db.c file, all other functions are implemented in a standalone 
database module. You will need to compile and link db.c in your module to be 
able to use the bind_dbmod function. Detailed function description follows.


2.1 Function bind_dbmod

2.1.1 Description

This function is special, it's only purpose is to call find_export function in
the ser core and find addresses of all other functions (starting with db_
prefix). This function MUST be called __FIRST__ !

2.1.2 Prototype

   int bind_dbmod(void);

2.1.3 Parameters

The function takes no parameters.

2.1.4 Return Value

The function returns 0 if it was able to find addresses of all other 
functions, otherwise value < 0 is returned.


2.2 Function db_init

2.2.1 Description

Use this function to initialize the database API and open a new database 
connection. This function must be called after bind_dbmod but before any other 
function is called.

2.2.2 Prototype

   db_con_t* db_init(const char* _sql_url);

2.2.3 Parameters

The function takes one parameter, the parameter must contain database 
connection URL. The URL is of the form 
sql://username:password@host:port/database where:

username: Username to use when logging into database (optional).
password: password if it was set (optional)
host:     Hosname or IP address of the host where database server lives 
          (mandatory)
port:     Port number of the server if the port differs from default value 
          (optional)
database: If the database server supports multiple databases, you must specify 
          name of the database (optional).


2.2.4 Return Value

The function returns pointer to db_con_t* representing the connection if it was
successful, otherwise 0 is returned.


2.3 Function db_close

2.3.1 Description

The function closes previously open connection and frees all previously 
allocated memory. The function db_close must be the very last function called.


2.3.2 Prototype

   void db_close(db_con_t* _h);

2.3.3 Parameters

The function takes one parameter, this parameter is a pointer to db_con_t
structure representing database connection that should be closed.

2.3.4 Return Value

Function doesn't return anything.


2.4 Function db_query

2.4.1 Description

This function implements SELECT SQL directive.

2.4.2 Prototype

   int db_query(db_con_t* _h, db_key_t* _k, db_op_t* _op,
                db_val_t* _v, db_key_t* _c, 
	        int _n, int _nc, db_key_t _o, db_res_t** _r);

2.4.3 Parameters

The function takes 7 parameters:
_h:  Database connection handle
_k:  Array of column names that will be compared and their values must match
_op: Array of operators to be used with key-value pairs
_v:  Array of values, columns specified in _k parameter must match these values
_c:  Array of column names that you are interested in
_n:  Number of key-value pairs to match in _k and _v parameters
_nc: Number of columns in _c parameter
_o:  Order by
_r:  Address of variable where pointer to the result will be stored

If _k and _v parameters are NULL and _n is zero, you will get the whole table.
if _c is NULL and _nc is zero, you will get all table columns in the result

_r will point to a dynamically allocated structure, it is neccessary to call
db_free_query function once you are finished with the result.

If _op is 0, equal (=) will be used for all key-value pairs.

Strings in the result are not duplicated, they will be discarded if you call
db_free_query, make a copy yourself if you need to keep it after db_free_query.

You must call db_free_query _BEFORE_ you can call db_query again !

2.4.4 Return Value

The function returns 0 if everything is OK, otherwise value < 0 is returned.


2.5 Function db_free_query

2.5.1 Description

This function frees all memory allocated previously in db_query, it is
neccessary to call this function on a db_res_t structure if you don't need the
structure anymore. You must call this function _BEFORE_ you call db_query
again !

2.5.2 Prototype

   int db_free_query(db_con_t* _h, db_res_t* _r);

2.5.3 Parameters

The function takes 2 parameters:
_h: Database connection handle
_r: Pointer to db_res_t structure to destroy

2.5.4 Return Value

The function returns 0 if everything is OK, otherwise the function returns
value < 0.


2.6 Function db_insert

2.6.1 Description

This function implements INSERT SQL directive, you can insert one or more
rows in a table using this function.

2.6.2 Prototype

   int db_insert(db_con_t* _h, db_key_t* _k, db_val_t* _v, int _n);

2.6.3 Parameters

The function takes 4 parameters:
_h: Database connection handle
_k: Array of keys (column names) 
_v: Array of values for keys specified in _k parameter
_n: Number of keys-value pairs int _k and _v parameters

2.6.4 Return Value

The function returns 0 if everything is OK, otherwise the function returns
value < 0.


2.7 Function db_delete

2.7.1 Description

This function implements DELETE SQL directive, it is possible to delete one or
more rows from a table.

2.7.2 Prototype

   int db_delete(db_con_t* _h, db_key_t* _k, db_op_t* _o, db_val_t* _v, int _n);

2.7.3 Parameters

The function takes 4 parameters:
_h: Database connection handle
_k: Array of keys (column names) that will be matched
_o: Array of operators to be used with key-value pairs
_v: Array of values that the row must match to be deleted
_n: Number of keys-value parameters in _k and _v parameters

If _k is NULL and _v is NULL and _n is zero, all rows are deleted (table will
be empty).

If _o is NULL, equal operator (=) will be used everywhere.

2.7.4 Return Value

The function returns 0 if everything is OK, otherwise the function returns
value < 0.


2.8 Function db_update

2.8.1 Description

The function implements UPDATE SQL directive. It is possible to modify one
or more rows in a table using this function.

2.8.2 Prototype

   int db_update(db_con_t* _h, db_key_t* _k, db_op_t* _o, db_val_t* _v,
	         db_key_t* _uk, db_val_t* _uv, int _n, int _un);

2.8.3 Parameters

The function takes 7 parameters:
_h: Database connection handle
_k: Array of keys (column names) that will be matched
_o: Array of operators to be used with key-value pairs
_v: Array of values that the row must match to be modified
_uk: Array of keys (column names) that will be modified
_uv: New values for keys specified in _k parameter
_n: Number of key-value pairs in _k and _v parameters
_un: Number of key-value pairs in _uk and _uv parameters 

2.8.4 Return Value

The function returns 0 if everything is OK, otherwise the function returns
value < 0.


2.9 Function db_use_table

2.9.1 Description

The function db_use_table takes a table name and stores it db_con_t structure.
All subsequent operations (insert, delete, update, query) are performed on
that table.

2.9.2 Prototype

   int db_use_table_f(db_con_t* _h, const char* _t);

2.9.3 Parameters

The function takes 2 parameters:
_h: Database connection handle
_t: Table name

2.9.4 Return Value

The function returns 0 if everything is OK, otherwise the function returns
value < 0.

