Another way to structure this problem is as sequences: 1. Start with a sequence of tables. (show-tables db-spec) 2. Filter down to only the tables you care about. (filter my-pred tables-seq) 3. Take only the first of these. (take 1 filtered-tables-seq) 4. If there is a table, do your side effects with it. (doseq [t 0-or-1-filtered-tables] (...))
That way, you will only do the work zero or one times, but the depth of your code is much shallower, and easier to read. e On Wed, Feb 25, 2015 at 1:35 PM, Cecil Westerhof <cldwester...@gmail.com> wrote: > 2015-02-25 19:23 GMT+01:00 Aaron Cohen <aa...@assonance.org>: > >> On Wed, Feb 25, 2015 at 1:08 PM, Cecil Westerhof <cldwester...@gmail.com> >> wrote: >> >>> >>> >>> 2015-02-25 18:14 GMT+01:00 Andy Fingerhut <andy.finger...@gmail.com>: >>> >>>> doseq does not have anything precisely like C/Java/Perl/etc.'s 'break' >>>> or 'continue'. The closest thing might be the :while keyword. You can see >>>> some one example of its use near the end of the examples on this page: >>>> http://clojuredocs.org/clojure.core/doseq >>>> >>>> The best way I know to get such behavior is to use Clojure's loop, >>>> where if/when/whatever-conditional-statements-you-wish can used to control >>>> explicitly to do another loop iteration using recur, or not. >>>> >>> >>> I made the following with loop: >>> (defn do-show-table >>> [table] >>> (loop [all-tables (show-tables db-spec)] >>> (let [this-table (get (first all-tables) :table_name)] >>> (if (= all-tables ()) >>> (printf "Table not found: %s\n" table) >>> (if (= (lower-case table) (lower-case this-table)) >>> (let [format "%-20s %-30s %-5s %-5s %-20s\n"] >>> (printf "Table %s:\n" table) >>> (printf format "Field" "Type" "Null?" "Key" "Default") >>> (doseq [{:keys [field type null key default]} >>> (jdbc/query db-spec [(str "SHOW COLUMNS FROM " >>> table)])] >>> >> >> Please don't get into the habit of doing db queries like this, you're one >> "Little Bobby Tables" away from an sql injection. In this case you should >> do (jdbc/query db-spec ["SHOW COLUMNS FROM ?" table]). >> > > That gives: > JdbcSQLException Syntax error in SQL statement "SHOW COLUMNS FROM ?"; > expected "identifier"; SQL statement: > SHOW COLUMNS FROM ? [42001-184] org.h2.engine.SessionRemote.done > (SessionRemote.java:622) > > > That is why I do it in this way. As I understood it this has to do with > that with a 'show columns from' the table can not be supplied. (I first > tried Yesql, only when that did not work I went to JDBC.) > > > > >> I think you would be well-served by a general clojure principle here of >> trying to get the data you're are dealing within into "values" as quickly >> as possible, and then working with those. >> >> Rather than inter-mixing your querying and display as you're doing here, >> I would design this as a query to fill some maps describing your tables, >> and then use clojure.pprint/print-table to print out the resulting map when >> desired. >> > > This was just a proof of concept to get things working in the REPL. Later > on it should be done much neater. (For example a text > > based version and a GUI version.) > > > >> (printf format field type null key default)) >> >>> >>> (println)) >>> (recur (rest all-tables))))))) >>> >>> It solves both problems. >>> >>> >>> On Wed, Feb 25, 2015 at 8:59 AM, Cecil Westerhof <cldwester...@gmail.com >>>> > wrote: >>>> >>>>> At the moment I have the following function: >>>>> (defn do-show-table >>>>> [table] >>>>> (doseq [{:keys [table_name]} (show-tables db-spec)] >>>>> (when (= (lower-case table) (lower-case table_name)) >>>>> (let [format "%-20s %-30s %-5s %-5s %-20s\n"] >>>>> (printf format "Field" "Type" "Null?" "Key" "Default") >>>>> (doseq [{:keys [field type null key default]} >>>>> (jdbc/query db-spec [(str "SHOW COLUMNS FROM >>>>> " table)])] >>>>> (printf format field type null key >>>>> default)))))) >>>>> >>>>> In this case it is not very important, because the outer sequence will >>>>> not be very big. But I would like to leave the doseq at the moment that >>>>> the >>>>> when is executed. It will be done 0 or 1 times, so after it is done, there >>>>> is no use in continuing the sequence walk. >>>>> >>>>> The second part is that I would like to do an action if it is done 0 >>>>> times after the doseq. Is this possible? >>>>> >>>> > -- > Cecil Westerhof > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
