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php-manual-zh-5.2.4-1mdv2008.1.noarch.rpm

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>章 45. PDO Driver How-To</TD
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><A
NAME="internals.pdo.pdo-dbh-t"
>pdo_dbh_t definition</A
></H1
><P
>&#13;  All fields should be treated as read-only by the driver, unless explicitly
  stated otherwise.
 </P
><DIV
CLASS="figure"
><A
NAME="AEN254353"
></A
><P
><B
>图 45-1. pdo_dbh_t</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
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><TR
><TD
><PRE
CLASS="c"
>/* represents a connection to a database */
struct _pdo_dbh_t {
    /* driver specific methods */
    struct pdo_dbh_methods *methods;    <A
NAME="internals.pdo.dbh.co.methods"
><IMG
SRC="../images/callouts/1.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(1)"></A
>
    /* driver specific data */
    void *driver_data;                  <A
NAME="internals.pdo.dbh.co.driver-data"
><IMG
SRC="../images/callouts/2.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(2)"></A
>

    /* credentials */
    char *username, *password;          <A
NAME="internals.pdo.dbh.co.credentials"
><IMG
SRC="../images/callouts/3.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(3)"></A
>

    /* if true, then data stored and pointed at by this handle must all be
     * persistently allocated */
    unsigned is_persistent:1;           <A
NAME="internals.pdo.dbh.co.is-persist"
><IMG
SRC="../images/callouts/4.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(4)"></A
>

    /* 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;             <A
NAME="internals.pdo.dbh.co.auto-commit"
><IMG
SRC="../images/callouts/5.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(5)"></A
>

    /* if true, the driver requires that memory be allocated explicitly for
     * the columns that are returned */
    unsigned alloc_own_columns:1;       <A
NAME="internals.pdo.dbh.co.alloc-own"
><IMG
SRC="../images/callouts/6.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(6)"></A
>

    /* 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;   <A
NAME="internals.pdo.dbh.co.max-esc"
><IMG
SRC="../images/callouts/7.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(7)"></A
>

    /* data source string used to open this handle */
    const char *data_source;            <A
NAME="internals.pdo.dbh.co.dsn"
><IMG
SRC="../images/callouts/8.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(8)"></A
>
    unsigned long data_source_len;

    /* the global error code. */
    pdo_error_type error_code;          <A
NAME="internals.pdo.dbh.co.error-code"
><IMG
SRC="../images/callouts/9.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(9)"></A
>

    enum pdo_case_conversion native_case<A
NAME="internals.pdo.dbh.co-ncase"
><IMG
SRC="../images/callouts/10.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(10)"></A
>, desired_case;
};</PRE
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><DIV
CLASS="calloutlist"
><DL
COMPACT="COMPACT"
><DT
><A
HREF="internals.pdo.pdo-dbh-t.html#internals.pdo.dbh.co.methods"
><IMG
SRC="../images/callouts/1.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(1)"></A
></DT
><DD
>&#13;    The driver <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>must</I
></SPAN
> set this during
    <B
CLASS="function"
>SKEL_handle_factory()</B
>.
   </DD
><DT
><A
HREF="internals.pdo.pdo-dbh-t.html#internals.pdo.dbh.co.driver-data"
><IMG
SRC="../images/callouts/2.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(2)"></A
></DT
><DD
>&#13;    This item is for use by the driver; the intended usage is to store a
    pointer (during <B
CLASS="function"
>SKEL_handle_factory()</B
>) 
    to whatever instance data is required to maintain a connection to
    the database.
   </DD
><DT
><A
HREF="internals.pdo.pdo-dbh-t.html#internals.pdo.dbh.co.credentials"
><IMG
SRC="../images/callouts/3.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(3)"></A
></DT
><DD
>&#13;    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.
   </DD
><DT
><A
HREF="internals.pdo.pdo-dbh-t.html#internals.pdo.dbh.co.is-persist"
><IMG
SRC="../images/callouts/4.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(4)"></A
></DT
><DD
>&#13;    If this is set to 1, then any data that is referenced by the
    dbh, including whatever structure your driver allocates,
    <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>MUST</I
></SPAN
> be allocated persistently.  This is easy to
    achieve; rather than using the usual <B
CLASS="function"
>emalloc()</B
> simply
    use <B
CLASS="function"
>pemalloc()</B
> 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.
   </DD
><DD
><P
>&#13;    If, for whatever reason, your driver is not suitable to run persistently,
    you <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>MUST</I
></SPAN
> check this flag in your
    <B
CLASS="function"
>SKEL_handle_factory()</B
> and raise an appropriate error.
   </P
></DD
><DT
><A
HREF="internals.pdo.pdo-dbh-t.html#internals.pdo.dbh.co.auto-commit"
><IMG
SRC="../images/callouts/5.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(5)"></A
></DT
><DD
>&#13;    You should check this value in your <B
CLASS="function"
>SKEL_handle_doer()</B
>
    and <B
CLASS="function"
>SKEL_stmt_execute()</B
> 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.
   </DD
><DT
><A
HREF="internals.pdo.pdo-dbh-t.html#internals.pdo.dbh.co.alloc-own"
><IMG
SRC="../images/callouts/6.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(6)"></A
></DT
><DD
>&#13;    If your database client library API operates by fetching data into a
    caller-supplied buffer, you should set this flag to 1 during your
    <B
CLASS="function"
>SKEL_handle_factory()</B
>.  When set, PDO will call your
    <B
CLASS="function"
>SKEL_stmt_describer()</B
> earlier that it would
    otherwise.  This early call allows you to determine those buffer sizes
    and issue appropriate calls to the database client library.
   </DD
><DD
><P
>&#13;    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.
   </P
></DD
><DT
><A
HREF="internals.pdo.pdo-dbh-t.html#internals.pdo.dbh.co.max-esc"
><IMG
SRC="../images/callouts/7.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(7)"></A
></DT
><DD
>&#13;    If your driver doesn't support native prepared statements
    (<CODE
CLASS="parameter"
>supports_placeholders</CODE
> is set to
    <TT
CLASS="constant"
><B
>PDO_PLACEHOLDER_NONE</B
></TT
>), you must set
    this value to the maximum length that can be taken up by a single
    character when it is quoted by your
    <B
CLASS="function"
>SKEL_handle_quoter()</B
> function.  This value is used to
    calculate the amount of buffer space required when PDO it executes the
    statement.
   </DD
><DT
><A
HREF="internals.pdo.pdo-dbh-t.html#internals.pdo.dbh.co.dsn"
><IMG
SRC="../images/callouts/8.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(8)"></A
></DT
><DD
>&#13;    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
    <B
CLASS="function"
>SKEL_handle_factory()</B
>.  Modifying this member should
    be avoided.  If you do change it, you must ensure that
    <CODE
CLASS="parameter"
>data_source_len</CODE
> is also correct.
   </DD
><DT
><A
HREF="internals.pdo.pdo-dbh-t.html#internals.pdo.dbh.co.error-code"
><IMG
SRC="../images/callouts/9.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(9)"></A
></DT
><DD
>&#13;    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 <B
CLASS="function"
>SKEL_handle_error()</B
> when an error is detected,
    and have it set the error code.
   </DD
><DT
><A
HREF="internals.pdo.pdo-dbh-t.html#internals.pdo.dbh.co-ncase"
><IMG
SRC="../images/callouts/10.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(10)"></A
></DT
><DD
>&#13;    Your driver should set this during
    <B
CLASS="function"
>SKEL_handle_factory()</B
>; 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
    <TT
CLASS="constant"
><B
>PDO_CASE_NATURAL</B
></TT
> (this is actually the default).
    If the column names are always returned in upper case, set it to
    <TT
CLASS="constant"
><B
>PDO_CASE_UPPER</B
></TT
>.  If the column names are always
    return in lower case, set it to <TT
CLASS="constant"
><B
>PDO_CASE_LOWER</B
></TT
>.
    The value you set it used to determine if PDO should perform case
    folding when the user sets the <TT
CLASS="constant"
><B
>PDO_ATTR_CASE</B
></TT
>
    attribute.
   </DD
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