Précédent 54. PDO Driver How-To Suivant

pdo_dbh_t definition

All fields should be treated as read-only by the driver, unless explicitly stated otherwise.

Figure 54.1. pdo_dbh_t

/* represents a connection to a database */
struct _pdo_dbh_t {
    /* driver specific methods */
    struct pdo_dbh_methods *methods;    
    /* driver specific data */
    void *driver_data;                  

    /* credentials */
    char *username, *password;          

    /* if true, then data stored and pointed at by this handle must all be
     * persistently allocated */
    unsigned is_persistent:1;           

    /* if true, driver should act as though a COMMIT were executed between
     * each executed statement; otherwise, COMMIT must be carried out manually
     * */
    unsigned auto_commit:1;             

    /* if true, the driver requires that memory be allocated explicitly for
     * the columns that are returned */
    unsigned alloc_own_columns:1;       

    /* if true, commit or rollBack is allowed to be called */
    unsigned in_txn:1;                  

    /* max length a single character can become after correct quoting */
    unsigned max_escaped_char_length:3;   

    /* data source string used to open this handle */
    const char *data_source;            
    unsigned long data_source_len;

    /* the global error code. */
    pdo_error_type error_code;          

    enum pdo_case_conversion native_case, desired_case;
};

1

The driver must set this during SKEL_handle_factory().

2

This item is for use by the driver; the intended usage is to store a pointer (during SKEL_handle_factory()) to whatever instance data is required to maintain a connection to the database.

3

The username and password that were passed into the PDO constructor. The driver should use these values when it initiates a connection to the database.

4

If this is set to 1, then any data that is referenced by the dbh, including whatever structure your driver allocates, MUST be allocated persistently. This is easy to achieve; rather than using the usual emalloc() simply use pemalloc() and pass the value of this flag as the last parameter. Failure to use the appropriate kind of memory can lead to serious memory faults, resulting (in the best case) a hard crash, and in the worst case, an exploitable memory problem.

If, for whatever reason, your driver is not suitable to run persistently, you MUST check this flag in your SKEL_handle_factory() and raise an appropriate error.

5

You should check this value in your SKEL_handle_doer() and SKEL_stmt_execute() functions; if it evaluates to true, you must attempt to commit the query now. Most database implementations offer an auto-commit mode that handles this automatically.

6

If your database client library API operates by fetching data into a caller-supplied buffer, you should set this flag to 1 during your SKEL_handle_factory(). When set, PDO will call your SKEL_stmt_describer() earlier than it would otherwise. This early call allows you to determine those buffer sizes and issue appropriate calls to the database client library.

If your database client library API simply returns pointers to its own internal buffers for you to copy after each fetch call, you should leave this value set to 0.

7

If your driver doesn't support native prepared statements (supports_placeholders is set to PDO_PLACEHOLDER_NONE), you must set this value to the maximum length that can be taken up by a single character when it is quoted by your SKEL_handle_quoter() function. This value is used to calculate the amount of buffer space required when PDO executes the statement.

8

This holds the value of the DSN that was passed into the PDO constructor. If your driver implementation needed to modify the DSN for whatever reason, it should update this member during SKEL_handle_factory(). Modifying this member should be avoided. If you do change it, you must ensure that data_source_len is also correct.

9

Whenever an error occurs during a call to one of your driver methods, you should set this member to the SQLSTATE code that best describes the error and return an error. In this HOW-TO, the suggested practice is to call SKEL_handle_error() when an error is detected, and have it set the error code.

10

Your driver should set this during SKEL_handle_factory(); the value should reflect how the database returns the names of the columns in result sets. If the name matches the case that was used in the query, set it to PDO_CASE_NATURAL (this is actually the default). If the column names are always returned in upper case, set it to PDO_CASE_UPPER. If the column names are always returned in lower case, set it to PDO_CASE_LOWER. The value you set is used to determine if PDO should perform case folding when the user sets the PDO_ATTR_CASE attribute.

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