How do I perform query filtering in django templates

Question

I need to perform a filtered query from within a django template  to get a set of objects equivalent to python code within a view   queryset   Modelclass objects filter somekey foo    In my template I would like to do     for object in data somekey set FILTER      but I just can t seem to find out how to write FILTER

User · Answer

This can be solved with an assignment tag   from django import template  register   template Library     register assignment tag def query qs    kwargs           template tag which allows queryset filtering  Usage               query books author author as mybooks                 for book in mybooks                                 endfor                return qs filter   kwargs

User · Answer

For anyone looking for an answer in 2020  This worked for me   In Views    class InstancesView generic ListView           model   AlarmInstance         context object name    settings context          queryset   Group objects all           template name    insta list html            register filter         def filter unknown self  aVal               result   aVal filter is known False              return result           register filter         def filter known self  aVal               result   aVal filter is known True              return result   In template      for instance in alarm qar alarm instances filter unknown alarm qar alarm instances      In pseudocode   For each in model child object view filter filter arg   Hope that helps

User · Answer

I run into this problem on a regular basis and often use the  add a method  solution  However  there are definitely cases where  add a method  or  compute it in the view  don t work  or don t work well   E g  when you are caching template fragments and need some non-trivial DB computation to produce it  You don t want to do the DB work unless you need to  but you won t know if you need to until you are deep in the template logic   Some other possible solutions    Use the    expr  lt expression  as  lt var name     template tag found at http   www djangosnippets org snippets 9  The expression is any legal Python expression with your template s Context as your local scope  Change your template processor  Jinja2  http   jinja pocoo org 2   has syntax that is almost identical to the Django template language  but with full Python power available  It s also faster  You can do this wholesale  or you might limit its use to templates that you are working on  but use Django s  safer  templates for designer-maintained pages

User · Answer

I just add an extra template tag like this    register filter def in category things  category       return things filter category category    Then I can do      for category in categories         for thing in things in category category           thing         endfor       endfor

User · Answer

You can t do this  which is by design   The Django framework authors intended a strict separation of presentation code from data logic   Filtering models is data logic  and outputting HTML is presentation logic   So you have several options   The easiest is to do the filtering  then pass the result to render to response   Or you could write a method in your model so that you can say    for object in data filtered set      Finally  you could write your own template tag  although in this specific case I would advise against that

User · Answer

I run into this problem on a regular basis and often use the  add a method  solution  However  there are definitely cases where  add a method  or  compute it in the view  don t work  or don t work well   E g  when you are caching template fragments and need some non-trivial DB computation to produce it  You don t want to do the DB work unless you need to  but you won t know if you need to until you are deep in the template logic   Some other possible solutions    Use the    expr  lt expression  as  lt var name     template tag found at http   www djangosnippets org snippets 9  The expression is any legal Python expression with your template s Context as your local scope  Change your template processor  Jinja2  http   jinja pocoo org 2   has syntax that is almost identical to the Django template language  but with full Python power available  It s also faster  You can do this wholesale  or you might limit its use to templates that you are working on  but use Django s  safer  templates for designer-maintained pages

User · Answer

The other option is that if you have a filter that you always want applied  to add a custom manager on the model in question which always applies the filter to the results returned   A good example of this is a Event model  where for 90  of the queries you do on the model you are going to want something like Event objects filter date  gte now   i e  you re normally interested in Events that are upcoming  This would look like   class EventManager models Manager       def get query set self           now   datetime now           return super EventManager self  get query set   filter date  gte now    And in the model   class Event models Model               objects   EventManager     But again  this applies the same filter against all default queries done on the Event model and so isn t as flexible some of the techniques described above

User · Answer

You can t do this  which is by design   The Django framework authors intended a strict separation of presentation code from data logic   Filtering models is data logic  and outputting HTML is presentation logic   So you have several options   The easiest is to do the filtering  then pass the result to render to response   Or you could write a method in your model so that you can say    for object in data filtered set      Finally  you could write your own template tag  although in this specific case I would advise against that

User · Answer

For anyone looking for an answer in 2020  This worked for me   In Views    class InstancesView generic ListView           model   AlarmInstance         context object name    settings context          queryset   Group objects all           template name    insta list html            register filter         def filter unknown self  aVal               result   aVal filter is known False              return result           register filter         def filter known self  aVal               result   aVal filter is known True              return result   In template      for instance in alarm qar alarm instances filter unknown alarm qar alarm instances      In pseudocode   For each in model child object view filter filter arg   Hope that helps

User · Answer

I run into this problem on a regular basis and often use the  add a method  solution  However  there are definitely cases where  add a method  or  compute it in the view  don t work  or don t work well   E g  when you are caching template fragments and need some non-trivial DB computation to produce it  You don t want to do the DB work unless you need to  but you won t know if you need to until you are deep in the template logic   Some other possible solutions    Use the    expr  lt expression  as  lt var name     template tag found at http   www djangosnippets org snippets 9  The expression is any legal Python expression with your template s Context as your local scope  Change your template processor  Jinja2  http   jinja pocoo org 2   has syntax that is almost identical to the Django template language  but with full Python power available  It s also faster  You can do this wholesale  or you might limit its use to templates that you are working on  but use Django s  safer  templates for designer-maintained pages

User · Answer

This can be solved with an assignment tag   from django import template  register   template Library     register assignment tag def query qs    kwargs           template tag which allows queryset filtering  Usage               query books author author as mybooks                 for book in mybooks                                 endfor                return qs filter   kwargs

User · Answer

I just add an extra template tag like this    register filter def in category things  category       return things filter category category    Then I can do      for category in categories         for thing in things in category category           thing         endfor       endfor

User · Answer

You can t do this  which is by design   The Django framework authors intended a strict separation of presentation code from data logic   Filtering models is data logic  and outputting HTML is presentation logic   So you have several options   The easiest is to do the filtering  then pass the result to render to response   Or you could write a method in your model so that you can say    for object in data filtered set      Finally  you could write your own template tag  although in this specific case I would advise against that

User · Answer

I run into this problem on a regular basis and often use the  add a method  solution  However  there are definitely cases where  add a method  or  compute it in the view  don t work  or don t work well   E g  when you are caching template fragments and need some non-trivial DB computation to produce it  You don t want to do the DB work unless you need to  but you won t know if you need to until you are deep in the template logic   Some other possible solutions    Use the    expr  lt expression  as  lt var name     template tag found at http   www djangosnippets org snippets 9  The expression is any legal Python expression with your template s Context as your local scope  Change your template processor  Jinja2  http   jinja pocoo org 2   has syntax that is almost identical to the Django template language  but with full Python power available  It s also faster  You can do this wholesale  or you might limit its use to templates that you are working on  but use Django s  safer  templates for designer-maintained pages

User · Answer

You can t do this  which is by design   The Django framework authors intended a strict separation of presentation code from data logic   Filtering models is data logic  and outputting HTML is presentation logic   So you have several options   The easiest is to do the filtering  then pass the result to render to response   Or you could write a method in your model so that you can say    for object in data filtered set      Finally  you could write your own template tag  although in this specific case I would advise against that

User · Answer

The other option is that if you have a filter that you always want applied  to add a custom manager on the model in question which always applies the filter to the results returned   A good example of this is a Event model  where for 90  of the queries you do on the model you are going to want something like Event objects filter date  gte now   i e  you re normally interested in Events that are upcoming  This would look like   class EventManager models Manager       def get query set self           now   datetime now           return super EventManager self  get query set   filter date  gte now    And in the model   class Event models Model               objects   EventManager     But again  this applies the same filter against all default queries done on the Event model and so isn t as flexible some of the techniques described above

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