A few days ago I faced a problem of evaluating dynamic expressions on domain objects. The scenario was that, depending upon the user input, I needed to sort a list of objects on some properties, which were nested deep in the object, e.g.,<\/p>\n
[java]
\nstudent.course?.college?.name \/\/ if a user chose to sort students by college name
\nstudent.course.teacher.name \/\/ if a user chose to sort students by teacher name.
\n[\/java]<\/p>\n
Using if, else could not have been an elegant solution, considering that there were many more fields to be sorted upon. This is when groovy.util.Eval class came to my notice. I found a useful function there:
\n[java]Eval.x(java.lang.Object x, java.lang.String expression)[\/java]<\/p>\n
Its usage is like this:<\/p>\n
[java]assert 10 == Eval.x(2, ‘ x * 4 + 2’)[\/java]<\/p>\n
and I wrote:<\/p>\n
[java]
\nstudents.sort {Eval.x(it, "x.${sortField}")} \/\/ sortField could be student.course?.college?.name
\n[\/java]<\/p>\n
In addition to this, groovy.util.Eval has some more useful methods like:<\/p>\n
[java]<\/p>\n
assert 10 == Eval.me(‘ 2 * 4 + 2’)
\nassert 10 == Eval.xyz(2, 4, 2, ‘ x * y + z’)
\nassert 10 == Eval.xy(2, 4, ‘ x * y + 2’)
\n[\/java]<\/p>\n
Hope this helps.
\nImran Mir
\nimran[@]intelligrape.com<\/p>\n","protected":false},"excerpt":{"rendered":"
A few days ago I faced a problem of evaluating dynamic expressions on domain objects. The scenario was that, depending upon the user input, I needed to sort a list of objects on some properties, which were nested deep in the object, e.g., [java] student.course?.college?.name \/\/ if a user chose to sort students by college […]<\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"iawp_total_views":50,"footnotes":""},"categories":[7],"tags":[896,895,894,4840,9],"class_list":["post-6549","post","type-post","status-publish","format-standard","hentry","category-grails","tag-eval","tag-evaluate","tag-expressions","tag-grails","tag-groovy"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t