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POnamed_scope in rails with a has_many association
 

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    <p>I am trying to achieve what I think will be a fairly complex query using the magic of Rails without having lots of ugly looking SQL in the code.</p> <p>Since my database is dealing with rather specialised biomedical models I'll translate the following to a more real world scenario. </p> <p>I have a model Book that</p> <p>has_many :chapters</p> <p>and Chapter that </p> <p>belongs_to :book</p> <p>Say for instance Chapters have a name attribute and the names can be preface ,introduction and appendix, and a Book could have a Chapter named preface and a Chapter named introduction but no Chapter named appendix. In fact any combination of these</p> <p>I am looking to find all Books that have both Chapters named preface and introduction.</p> <p>At present I have a named_scope as follows</p> <pre><code>Book named_scope :has_chapter?, lambda { |chapter_names| condition_string_array = [] chapter_names.size.times{condition_string_array &lt;&lt; "chapters.name = ?"} condition_string = condition_string_array.join(" OR ") {:joins =&gt; [:chapters] , :conditions =&gt; [condition_string, * chapter_names]} } </code></pre> <p>If I call Book. has_chapter? ["preface", "introduction"] this will find me all books that have either a Chapter named preface or introduction. How could I do a similar thing that would find me isolates that <strong>both</strong> Chapters preface and introduction?</p> <p>I am not that familiar with SQL so am not quite sure what kind of join would be needed and whether this could be achieved in a named scope.</p> <p>Many thanks</p> <p>Anthony</p>
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