The README Aug 6th, 2015   [viewed 3719 times]

MVProc is a Model-View-Controller web framework that uses MySQL stored procedures as the controller element. It is implemented as an Apache2 module, mod_mvproc.

There are currently no plans to implement this for any other database, as no other database has enough flexibility of functionality in the context of stored routines. (At least as far as I'm aware.)


The Makefile and #includes section of mvproc.h may need to be edited before compiling, specifically the APACHE_HOME variable and location of apr-1 and apreq2. It will build on Ubuntu, but other distros may have different locations of headers and libs (eg. /usr/lib64 instead of /usr/lib).

Required Packages: apache2-dev, libapr1-dev


Since mod_mvproc is a module it must be loaded in your apache configuration file. apreq_module is required and must be loaded prior to loading mvproc, like so:

  • LoadModule apreq_module /usr/lib/apache2/modules/
  • LoadModule mvproc_module /usr/lib/apache2/modules/

There are thirteen (13) configuration directives for mod_mvproc:

mvprocSession (Y or N) - sets session behavior. If sessions are enabled (Y), the module will supply called stored procedures with a user variable @mvp_session, which will contain a 32 character session id. A cookie will be produced and maintained with this id as its value. The procedure may set the @mvp_session value, which will update the value of the cookie. The value is also included in the output of the call in the PROC_OUT section.

mvprocDbGroup (yourDBgroup) - this is the group in mysql's my.cnf file which mvproc will use to authenticate and connect to the database. An example:
host = localhost
port = 3306
user = myuser
password = mypass
database = webdb

Please refer to the MySQL documentation for my.cnf subtleties. Do consider that my.cnf is accessible. Best practice is to create a user (let's say 'foo'@'localhost') for an MVProc database (let's say `bar`) and grant only minimal access. Most of the time, this would be:
GRANT SELECT (`name`,`param_list`,`db`,`type`) ON `mysql`.`proc` TO 'foo'@'localhost';
(The above is the minimum required permission for MVProc to work at all.)
GRANT EXECUTE ON `bar`.* TO 'foo'@'localhost';

mvprocTemplateDir (/your/template/directory) - the location of the templates. This is best placed outside the doc root - in fact, if the template files are in the doc root Apache will get confused, thinking it should serve the file instead of allowing mvproc to handle the transaction. If mvprocTemplateDir is not set, or set with an empty string, templates and layouts will not be used. More on templates later.

mvprocDefaultLayout (yourLayoutTemplate - leave off the '.tpl') If set, this will set the @mvp_layout session variable to a default value. It's not required to set this in the configuration, as procedures can set it as well. More on layouts later.

mvprocDefaultProc (yourDefaultProc) If set, this will be the procedure that's called when the request uri is '/' or if the uri does not match a procedure. A non-proc uri is allowed so pages can be given interesting urls like Do remember to handle possible non-proc uris in your default proc. In order to force Apache to send '/' to mvproc, use


mvprocCache (Y or N) - Y enables caching of procs AND templates. Set to N during development and Y for production use.

mvprocDbPoolSize (number) - The number of connections to pool. If this is not set, or set to zero, a new connection will be established, used, and closed for each request.

mvprocOutputStyle (MIXED | PLAIN | JSON | EASY_XML | EASY_JSON) see the Output section below.

mvprocErrTemplate - If mvprocTemplateDir is configured, this is the name of the template to render when there's a database error. The error can be accessed as <# status.error #>.

mvprocAllowSetContent (Y or N) - provides @mvp_content_type session variable, which allows a procedure to tell Apache how to set the Content-Type header.

mvprocAllowHTMLfromDB (Y or N) – default N, Y allows HTML output from the database to be rendered as HTML. By default, MVProc will convert '<' to '<', '&' to '"', etc.

mvprocUploadDirectory - Sets the path to a directory where uploaded files are written. It is highly recommended that this path be OUTSIDE the docroot. If the path doesn't exist, MVProc will attempt to create it. Default value is /tmp

mvprocUserVars - a comma-delimited set of additional user vars to make available for output from the procs. This is useful when procs CALL each other and SET @mvp_template. Add no whitespace. Example: mvprocUserVars err,inset_include,universal_out


Requests are typical “pretty” web format, like so: If the url points to a file that exists, the module will decline handling, which means the file will be served as normal. If the uri is empty (ie. nothing or '/' after the url) or the uri does not match a stored procedure, the procedure specified by the mvprocDefaultProc configuration directive or 'landing' will be looked for. See mvprocDefaultProc config

GET and POST requests are supported, as well as file uploads. A file upload will be written to the system's temp directory with a pseudo-random name plus the original file extension. This filename will be reported to the procedure through the uploaded file's variable name. So a file-type input with name="myfile" will send something like '/tmp/87YHF228FA.jpg' into the procedure as the IN or INOUT argument 'myfile', but ONLY IF THE ARGUMENT EXISTS in the procedure's definition.


All aspects of MySQL stored procedures are supported. IN, INOUT, OUT parameters and multiple result sets are available to the template parser and are shown in xml output. User variables available to procedures are currently:

  • @mvp_servername - the server hostname (
  • @mvp_requestmethod - GET, POST, or REQUEST
  • @mvp_uri - the unparsed uri of the request
  • @mvp_template - by default, the procedure name - this value can be changed in the procedure to tell the module to use a different template file. This can be 'procname' or 'myother_template' or even (under the template directory) 'my_subdirectory/my_other_sub/even_farther/as_deep_as_you_like/template_name' Remember to leave off the '.tpl'
  • @mvp_layout - the layout template to use - this value can be set or changed in the procedure. Handling is essentially the same as for @mvp_template.
  • @mvp_headers - the HTTP headers
  • @mvp_remoteip - the requestor's ip address
  • @mvp_session - (if mvprocSession = 'Y') the current value of the MVPSESSION cookie This can be set in the procedure, but the module will set it up and provide a value by default. Once overridden, the set value will be returned with each subsequent request. (Just like a session... heh.) You could even store data in the cookie if it's ok for everyone to see. The only size limit is what a browser will actually send and receive in a cookie.
  • @mvp_content_type - (if mvprocAllowSetContent = 'Y') - This is passed in as an empty string. It's only used in output if set by the procedure.

Known Issues

Returning multiple result sets with the same table name causes libmysqlclient to seg fault. This includes calculated selects. So if you want to do this:

       SELECT 'a value' AS one_value; SELECT 'more value' AS too_value;

Instead, do this:

       SELECT 'a value' AS one_value, 'more value' AS too_value;

And if you want to return multiple result sets from the same table, use aliases.

If libmysqlclient starts to allow multiple result sets from the same table, be cautious about using EASY_XML and EASY_JSON output. The results are, at this point, undefined.


XML MIXED is the default output of a request. If no template exists, the module goes with this. Result sets are rendered in xml as a

element with child elements.

For the MIXED output type, columns whose declared size is 32 or less (for example VARCHAR(24)) are shown as attributes of rows, while blobs and columns of greater size (like VARBINARY(4096) or CHAR(65)) are shown as children of rows with CDATA encapsulated values.

The PLAIN output type populates the name attribute of the table tags, but all columns are rendered as CDATA encapsulated child elements.

Another option is JSON, which outputs an array of objects named 'table', each of which owns a name value and an array of row objects each of which owns one named value per column. Most ajax libraries support this format.

EASY_XML is the PLAIN type, except that instead of

elements, the output is written like . This may cause problems if multiple result sets from the same table are output.

EASY_JSON is JSON, except that instead of an array of objects named 'table', the output is an object with each result set as an element named for its table. This may cause problems if multiple result sets from the same table are output.

All result sets are output, as well as a “table” called PROC_OUT, which holds all INOUT and OUT values as well as mvp_session and mvp_template values. If a table is not declared in a select out (eg. SELECT 'whatever' AS myval) the table will be called “status”.

Here's an example of MIXED:

Errors will look like this:


Templates are typically html pages with tags for the parser to use to plug in values, loop through result sets, conditionally show or not show markup, include other templates. Some simple rules:

  • - an MVProc tag looks like this: <# the tag is in here #>.
  • - String literals are between single quotes.
  • - Inside single quotes you can have any characters you want - the quotes escape everything.
  • - Escape single quotes within single quotes with a backslash: \'
  • - The tag names must be either ALL CAPS (ELSEIF) or all lower (elseif).

The template tags are intentionally few in number. It encourages separation of concern.

Value - <# [table.]field_name[[row_num]] #>
The default table is PROC_OUT, and the default row_num is 0. Inside a LOOP, the default table becomes the LOOP table and the default row becomes the LOOP's CURRENT_ROW.
CURRENT_ROW (all caps) is a built-in value of type INT (actually unsigned long in C terms).
NUM_ROWS (all caps) is a built-in value of type INT accessed like: <# IF tableName.NUM_ROWS > 0 #>
The '@' table holds user variables for the templates (see SET).

IF - <# IF myvar = 'hello' #>
Supported comparison operators are: =, ==, !=, !, <>, <, >, <=, and >=
With no operator, a value equals true if non-zero (int & float) or non-empty (string).
The not operator (!) equals true if zero (int & float) or empty (string).
Nesting is supported, as well as AND, and, OR, or, &&, and ||
AND, and, and && take precedence over OR, or, and ||
Example: <# IF mytable.what[2] = 'ok' AND (CURRENT_ROW > 4 OR !@.checkit) #>
Nesting is arbitrarily limited to a depth of 64.
No math is supported in IF tags.
Constants are supported: strings are quoted with single quotes and floats must have a '.' (eg 0.0)

ELSIF - <# ELSIF @.val_is_set #> - Identical parsing and evaluation to IF.

ELSE - <# ELSE #> - This functions as anyone would expect.

ENDIF - <# ENDIF #> - Again, like anyone would expect. This tag is REQUIRED with IF usage.

LOOP - <# LOOP mytable #>
The LOOP tag begins a template segment that will iterate once for each row in a result set.
Inside the LOOP, the table specified becomes the default table, and CURRENT_ROW will evaluate to the current row (zero indexed).

ENDLOOP - <# ENDLOOP #> - Closes a loop. This tag is REQUIRED for each LOOP started.

INCLUDE - <# INCLUDE another_template #>
The specified template will be included at the tag's position.
The included template is referenced from the configured mvprocTemplateDir, so if your template directory is /var/templates and you <# INCLUDE layouts/header #>, the file looked for will be /var/templates/layouts/header.tpl
Always leave the '.tpl' off the include argument.
INCLUDE can also accept a value tag like: <# INCLUDE myTable.myValue[4] #>

TEMPLATE - <# TEMPLATE #> - This is essentially an include tag, except that it uses the @mvp_template session variable. Use this convenience tag inside a layout template.

SET - <# SET myvar = 'ok' #>
One could create a very rich site with lots of functionality without using this tag. I haven't benchmarked the difference between setting all required values in the procedure vs. setting some in the template but I suspect SET might be a bit slower, and it's certainly less efficient with memory. That being said, is it available.

  • - The SET tag sets a value in the '@' table, which supports only one row.
  • - <# SET row_class = 'color' + CURRENT_ROW % 2 + 1 #> would be referenced
  • - <# @.row_class #> (and this is useful for alternating row css style)
  • - Supported operators are =, +, -, *, /, %, and comma(,)
  • - String “math” supports only concatenation (+), ints and floats use C-style math.
  • - *, /, and % take precedence over + and -.
  • - Modulus (%) evaluates to the remainder for int values and the fraction for floats.
  • - Constants are supported: strings are quoted with single quotes and floats must have a '.' (eg 0.0)
  • - The comma is for multiple assignments in a tag, like so: <# SET a = 0, b = 'hi', c = @.a / 1 #>

CALL - <# CALL procname([comma-separated args]) [INTO] tablename(s) #>
I hesitated for about five years to add something like this to MVProc –  there is no reason whatsoever to ever use this tag. Or is there...?  In any case, it's easy to use.

  • - 'procname' would, of course, be the name of the procedure to call, followed by the argument list in parentheses.
    - 'INTO' is optional and states the table names to insert the result set(s) into.
    - For arguments, if you don't supply enough arguments, MVProc will send empty values to the procedure. If you supply too many, the extras will be ignored. Arguments themselves are value tags, so PROC_OUT.myval will send the contents of PROC_OUT.myval and such, just like the value tag. To send a literal, enclose in single quotes like 'my argument!' - and just like the IF and SET tags (and others) escape single quotes with a backslash.
    - The optional INTO declaration works the same way as arguments, in that extra values supplied will be ignored, and if more result sets come from the procedure than names are supplied, the table names will be used (just like the main procedure call). Also like arguments, you can supply table names from value tags or literal values.
    - CALL works a bit differently than the main procedure call in that all input values to the procedure must be declared by the procedure definition and listed with the parameters. For example, the @mvp_session variable is not supplied unless you specifically pass it into the procedure as an argument. (UserVars are, however, available for undeclared output from the procedure.) Instead of PROC_OUT holding the parameters from OUT, INOUT, and UserVars, the default name of that result of the CALL output is named 'PARAMS_OUT'
    - When results are returned from the CALLed procedure, any table names identical to already existing results in the templates' data structure will be replaced. So if your main procedure returns 'vendors', 'products', and PROC_OUT data, then you call another procedure that outputs 'vendors' and PARAMS_OUT, you'll lose access to the original 'vendors' result set. This is the reason for the INTO declaration.
    - As a final word on the CALL tag, I can say without reservation that use of it can be the most wasteful, inefficient, and unnecessary exercise to undertake with MVProc. Always consider whether there'sa way to have things handled in the main procedure call. The inefficiency is more than just the CPU and memory cost of the queries. It uses a connection from the connection pool, MySQL has to parse the incoming request, data structures have to be alloc'ed and eventually de-alloc'ed... so if you have an MVProc site that uses CALL liberally and seems to be running slowly, LOOK THERE FIRST.
    - And, of course, I'm sizing up a project that will use CALL. Wish me luck.


And that's it.

I think. Any questions, bugs, requests - please post on

-Jeff Walter

maintainer, MVProc