Check if a string is null or empty in XSLT

Question

How can I check if a value is null or empty with XSL   For example  if categoryName is empty  I m using a when choosing construct   For example    lt xsl choose gt       lt xsl when test  categoryName   null  gt           lt xsl value-of select  categoryName     gt       lt  xsl when gt       lt xsl otherwise gt           lt xsl value-of select  other    gt       lt  xsl otherwise gt   lt  xsl choose gt

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Absent of any other information  I ll assume the following XML    lt group gt       lt item gt           lt id gt item 1 lt  id gt           lt CategoryName gt blue lt  CategoryName gt       lt  item gt       lt item gt           lt id gt item 2 lt  id gt           lt CategoryName gt  lt  CategoryName gt       lt  item gt       lt item gt           lt id gt item 3 lt  id gt       lt  item gt           lt  group gt    A sample use case would look like    lt xsl for-each select   group item  gt       lt xsl if test  CategoryName  gt           lt  -- will be instantiated for item  1 and item  2 -- gt       lt  xsl if gt       lt xsl if test  not CategoryName   gt           lt  -- will be instantiated for item  3 -- gt       lt  xsl if gt       lt xsl if test  CategoryName        gt           lt  -- will be instantiated for item  1 -- gt       lt  xsl if gt       lt xsl if test  CategoryName       gt           lt  -- will be instantiated for item  2 -- gt       lt  xsl if gt   lt  xsl for-each gt

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I know this question is old  but between all the answers  I miss one that is a common approach for this use-case in XSLT development   I am imagining that the missing code from the OP looks something like this    lt xsl template match  category  gt       lt xsl choose gt           lt xsl when test  categoryName   null  gt               lt xsl value-of select  categoryName     gt           lt  xsl when gt           lt xsl otherwise gt               lt xsl value-of select  other    gt           lt  xsl otherwise gt       lt  xsl choose gt   lt  category gt    And that the input looks something like this    lt categories gt       lt category gt          lt categoryName gt Books lt  categoryName gt       lt  category gt       lt category gt          lt categoryName gt Magazines lt  categoryName gt          lt categoryName gt Periodicals lt  categoryName gt          lt categoryName gt Journals lt  categoryName gt       lt  category gt       lt category gt           lt categoryName gt  lt  -- please fill in category -- gt  lt  categoryName gt       lt  category gt       lt category gt           lt categoryName   gt       lt  category gt       lt category   gt   lt  categories gt    I e   I assume there can be zero  empty  single or multiple categoryName elements  To deal with all these cases using xsl choose-style constructs  or in other words  imperatively  is quickly getting messy  even more so if elements can be at different levels    A typical programming idiom in XSLT is using templates  hence the T in XSLT   which is declarative programming  not imperative  you don t tell the processor what to do  you just tell what you want output if certain conditions are met   For this use-case  that can look something like the following    lt  -- positive test  any category with a valid categoryName -- gt   lt xsl template match  category categoryName text      gt       lt xsl apply-templates   gt   lt  xsl template gt    lt  -- any other category  without categoryName   null   with comments etc  -- gt   lt xsl template match  category  gt       lt xsl text gt Category  Other lt  xsl text gt   lt  xsl template gt    lt  -- matching the categoryName itself for easy handling of multiple names -- gt   lt xsl template match  categoryName  gt       lt xsl text gt Category   lt  xsl text gt       lt xsl value-of select       gt   lt  xsl template gt    This works  with any XSLT version   because the first one above has a higher precedence  it has a predicate   The  fall-through  matching template  the second one  catches anything that is not valid  The third one then takes care of outputting the categoryName value in a proper way    Note that in this scenario there is no need to specifially match categories or category  because the processor will automatically process all children  unless we tell it otherwise  in this example  the second and third template do not further process the children  because there is no xsl apply-templates in them    This approach is more easily extendible then the imperative approach  because it automically deals with multiple categories and it can be expanded for other elements or exceptions by just adding another matching template  Programming without if-branches   Note  there is no such thing as null in XML  There is xsi nil  but that is rarely used  especially rarely in untyped scenarios without a schema of some sort

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Use simple categoryName text   Such test works fine on  lt categoryName  gt  and also  lt categoryName gt  lt  categoryName gt     lt xsl choose gt       lt xsl when test  categoryName text    gt           lt xsl value-of select  categoryName    gt       lt  xsl when gt       lt xsl otherwise gt           lt xsl value-of select  other    gt       lt  xsl otherwise gt   lt  xsl choose gt

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If there is a possibility that the element does not exist in the XML I would test both that the element is present and that the string-length is greater than zero    lt xsl choose gt       lt xsl when test  categoryName and string-length categoryName   amp gt  0  gt           lt xsl value-of select  categoryName     gt       lt  xsl when gt       lt xsl otherwise gt           lt xsl value-of select  other    gt       lt  xsl otherwise gt   lt  xsl choose gt

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Something like this works for me    lt xsl choose gt     lt xsl when test  string number categoryName      NaN   gt  -  lt  xsl when gt      lt xsl otherwise gt        lt xsl number value  categoryName    gt     lt  xsl otherwise gt   lt  xsl choose gt    Or the other way around    lt xsl choose gt     lt xsl when test  string number categoryName       NaN   gt       lt xsl number value  categoryName    gt     lt  xsl when gt      lt xsl otherwise gt  -  lt  xsl otherwise gt   lt  xsl choose gt    Note  If you don t check null values or handle null values  IE7 returns -2147483648 instead of NaN

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I actually found it better just testing for string length since many times the field is not null  just empty       lt xsl when test  string-length field-you-want-to-test  lt 1

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In some cases  you might want to know when the value is specifically null  which is particularly necessary when using XML which has been serialized from  NET objects   While the accepted answer works for this  it also returns the same result when the string is blank or empty  i e      so you can t differentiate    lt group gt       lt item gt           lt id gt item 1 lt  id gt           lt CategoryName xsi nil  true    gt       lt  item gt   lt  group gt    So you can simply test the attribute    lt xsl if test  CategoryName  xsi nil  true   gt     Hello World   lt  xsl if gt    Sometimes it s necessary to know the exact state and you can t simply check if CategoryName is instantiated  because unlike say Javascript   lt xsl if test  CategoryName  gt     Hello World   lt  xsl if gt    Will return true for a null element

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First two deal with null value and second two deal with empty string    lt xsl if test  USER FIRSTNAME  gt      USERNAME is not null  lt  xsl if gt   lt xsl if test  not USER FIRSTNAME   gt      USERNAME is null   lt  xsl if gt    lt xsl if test  USER FIRSTNAME     gt       USERNAME is empty string   lt  xsl if gt    lt xsl if test  USER FIRSTNAME      gt       USERNAME is not empty string   lt  xsl if gt

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By my experience the best way is    lt xsl when test  not string categoryName    gt       lt xsl value-of select  other    gt   lt  xsl when gt   lt otherwise gt       lt xsl value-of select  categoryName    gt   lt  otherwise gt

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How can I check if a value is null or empty with XSL       For example  if categoryName is empty    This is probably the simplest XPath expression  the one in accepted answer provides a test for the opposite  and would be longer  if negated    not string categoryName     Explanation   The argument to the not   function above is false   exactly when there is no categoryName child   null   of the context item  or the  single such  categoryName child has string value -- the empty string      I m using a when choosing construct       For example    lt xsl choose gt       lt xsl when test  categoryName   null  gt           lt xsl value-of select  categoryName     gt       lt  xsl when gt       lt xsl otherwise gt           lt xsl value-of select  other    gt       lt  xsl otherwise gt   lt  xsl choose gt     In XSLT 2 0 use    lt xsl copy-of select  concat categoryName    vOther not string current   categoryName       gt    Here is a complete example    lt xsl stylesheet version  2 0  xmlns xsl  http   www w3 org 1999 XSL Transform  gt        lt xsl output omit-xml-declaration  yes  indent  yes   gt     lt xsl variable name  vOther  select   Other    gt     lt xsl template match     gt     lt xsl copy-of select  concat categoryName  vOther not string current   categoryName       gt    lt  xsl template gt   lt  xsl stylesheet gt    When this transformation is applied on the following XML document    lt categoryName gt X lt  categoryName gt    the wanted  correct result is produced   X   When applied on this XML document    lt categoryName gt  lt  categoryName gt    or on this    lt categoryName  gt    or on this   lt somethingElse gt Y lt  somethingElse gt    the correct result is produced   Other     Similarly  use this XSLT 1 0 transformation    lt xsl stylesheet version  1 0  xmlns xsl  http   www w3 org 1999 XSL Transform  gt    lt xsl output omit-xml-declaration  yes  indent  yes   gt     lt xsl variable name  vOther  select   Other    gt      lt xsl template match     gt       lt xsl copy-of select       concat categoryName   substring  vOther  1 div not string categoryName       gt     lt  xsl template gt   lt  xsl stylesheet gt    Do note  No conditionals are used at all  Learn more about the importance of avoiding conditional constructs in this nice Pluralsight course    Tactical Design Patterns in  NET  Control Flow

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test  categoryName          Edit  This covers the most likely interpretation  in my opinion  of   not  null or empty  as inferred from the question  including it s pseudo-code and my own early experience with XSLT  I e    What is the equivalent of the following Java       categoryName    null    categoryName equals        For more details e g   distinctly identifying null vs  empty  see johnvey s answer below and or the XSLT  fiddle  I ve adapted from that answer  which includes the option in Michael Kay s comment as well as the sixth possible interpretation

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If a node has no value available in the input xml like below xpath    lt node gt       lt ErrorCode  gt   lt  node gt    string   function converts into empty value  So this works fine   string  Node ErrorCode

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From Empty Element   To test if the value of a certain node is empty  It depends on what you mean by empty    Contains no child nodes  not node    Contains no text content  not string     Contains no text other than whitespace  not normalize-space     Contains nothing except comments  not node   not self  comment

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What about   test  not normalize-space categoryName

[xslt] Check if a string is null or empty in XSLT

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