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Limitations on Filter for Table Lookup

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    #1

    Limitations on Filter for Table Lookup

    Is there a limitation on how many filters work?

    This works:
    COUNTY1"Do Not Use" .and. Dr_Id_Number Client->DnuDr1 .and. Dr_Id_Number Client->Dnu_Dr2 .and. Dr_Id_Number Client->Dnu_Dr3
    This does not:
    COUNTY1"Do Not Use" .and. Dr_Id_Number Client->DnuDr1 .and. Dr_Id_Number Client->Dnu_Dr2 .and. Dr_Id_Number Client->Dnu_Dr3 .and. Dr_Id_NumberClient->Dnu_Dr4
    Tags: None
    #2
    RE: Limitations on Filter for Table Lookup

    If memory serves there's a problem with using filtered table lookups by field rule. Others have had better success creating a custom form and using it as the lookup source.

    -- tom

    Comment

      #3
      RE: Limitations on Filter for Table Lookup

      I'm not sure if there is a limitation or not, but you might see if this works.

      COUNTY1"Do Not Use" .and. .not.
      inlist(Dr_Id_Number,Client->DnuDr1,Client->Dnu_Dr2,
      Client->Dnu_Dr3,Client->Dnu_Dr4)

      Comment

        #4
        RE: Limitations on Filter for Table Lookup

        Thanks John,

        COUNTY1"Do Not Use" .and. .not.
        inlist(Dr_Id_Number,Client->DnuDr1,Client->Dnu_Dr2,
        Client->Dnu_Dr3,Client->Dnu_Dr4)
        Does not work, but,
        COUNTY1"Do Not Use" .and. .not.
        inlist(Dr_Id_Number,Client->DnuDr1,Client->Dnu_Dr2,
        Client->Dnu_Dr3)
        Does

        Guess there is a limitation.

        Comment

          #5
          RE: Limitations on Filter for Table Lookup

          If there is a length limit you could create a variable (vFilter) in table definition and give it the value of your filter. The use vFilter as your lookup filter.

          For sure you can use a variable in a table lookup filter expression.

          Bill
          Bill Hanigsberg

          Comment

            #6
            RE: Limitations on Filter for Table Lookup

            Bill,

            I thought about that but the following is a notation on variables...

            "NOTE Variables cannot be used with the Lookup Field Rule."

            Will it work anyway? And how would I define the variable to be the filter?

            - Elke

            Comment

              #7
              RE: Limitations on Filter for Table Lookup

              Elke,

              Where did you read that? Anyway, you can use variables in lookup filter expressions, to a point anyway.

              I created a variable vGender and successfully used the expression gender=vGender as a table lookup filter in field rules.

              However I was not able to include an entire filter expression in a variable and then use that variable (vFilter in the attached example) as the whole filter expression. (And yes, I tried the expression eval(vFilter) as well although *it did evaluate correctly in the expression builder* it would not save.)

              So that's as far as I took it.

              Bill
              Bill Hanigsberg

              Comment

                #8
                RE: Limitations on Filter for Table Lookup

                Bill Elke,
                I don't agree with using a variable in a lookup filter. What Alpha does is automatically build an index for the filter with the filter expression as a part of the index. If the variable value is changing, then the index will have to be rebuilt ( blue bars etc. ). In a multi-user environment I think you will eventually have some bad situations as the index has to be rebuilt with the table opened by others.

                What if you create a calulated field which is the concatenation of the three or four doctors. Then your filter could be a search for the doctor using an Alpha function that will investigate the existence of a specific string within the concatenated field. Bill does something like that in his example in the Learning Forum.
                John

                Comment

                  #9
                  RE: Limitations on Filter for Table Lookup

                  Hi John,

                  You may have a point about a lookup which is volatile but bear in mind that if the query can be optimized its generation will be instantaneous. That has been my experience, and in a multi-user environment. On the other side, Elke's expression wouldn't optimize.

                  Here is where I use a variable in a lookup:

                  In my scheduling software a department chair is associating teachers with a course. The teacher is picked from a lookup. The lookup is filtered to show only that department's teachers. The user's department number is held in a global variable initialized as part of the logon. So the filter is simple,
                  Dept=vDept
                  and is instant.

                  The teacher table has about 1500 records and is not particularly volatile although not absolutely static. There are about 25 simultaneous users.

                  Bill
                  Bill Hanigsberg

                  Comment

                    #10
                    RE: Limitations on Filter for Table Lookup

                    John,

                    Thought about that too, but there are really 20 fields not just four. Each field is an eight digit numeric field. Highest number of char. in a numeric field is 19...

                    Bill,

                    The note on variables is at the bottom of the help section on variables.

                    Comment

                      #11
                      RE: Limitations on Filter for Table Lookup

                      Bill,
                      I'm glad you have had a good experience with this. It's been my experience that lookups with filters ( not using variables just constants ) are more prone to problems than without filters.I guess that's because a filtered index is created and they are more prone to problems.I tried what you are doing and experienced enough problems to discourage me, but after retesting I see that when a simple filter with a variable filter like "state = var->currstate" Alpha does a query and can take advantage of optimization. I'm curious if Selwyn considers this to be a reliable method.Thanks for the explanation.
                      John

                      Comment

                        #12
                        RE: Limitations on Filter for Table Lookup

                        Elke,
                        Since you have up to 20 fields, you might want to set up a calculated field in the table which is a concatenation of the 20 fields (i.e. field1+field2+field3, etc) and then do your filter using the instr() function. That way you are only looking at one field.
                        Pat Bremkamp
                        MindKicks Consulting

                        Comment

                          #13
                          RE: Limitations on Filter for Table Lookup

                          Pat,

                          I couldn't use or find instr() function however

                          CONTAINS(CALC->drdnu,(str(Dr_Id_Number)))=.F.

                          works great.

                          Thank you.

                          Comment

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