grails - 防止在条件语句中使用条件过滤器

Question

我正在尝试做的一个例子是:

def authorName = "John Smith"
def books = Book.createCriteria().list() {
    eq('genre', 'fiction')
    eq('publishDate', '2007')
    if(authorName != null){
        Author author = Author.findWhere(name: authorName)
        if( author == null ) //what do I do here? 
        else { eq('authorId', author.id } 
    }
}

如果没有给定ID的作者，则该作者不存在(假设未删除)，因此该作者也没有写书。评估应在此处停止，并且不返回任何结果。我可以用什么来做到这一点？

Answer 1

我不是100％的尝试。如果您只想在作者存在的情况下执行Book查询，则可以这样...

def authorName = "John Smith"
Author author = Author.findWhere(name: authorName)
def books
if(author) {
    books = Book.withCriteria {
        eq('genre', 'fiction')
        eq('publishDate', '2007')

        // I can't tell if this is the right thing because
        // I don't know what your model looks like, but I will
        // assume this part is valid because it is what you had
        // in your example.
        eq 'authorId', author.id
    }
}

根据模型的外观，您还可以只将authorName作为条件的一部分，这样就不必执行2个查询了。

def authorName = "John Smith"
def books = Book.withCriteria {
    eq('genre', 'fiction')
    eq('publishDate', '2007')
    // this assumes that Book has a property named 
    // "author" which points to the Author
    author {
        eq 'name', authorName
    }
}