topic Re: tMap Expression always return false when passing a string expression using context variable in Talend Studio

tMap Expression always return false when passing a string expression using context variable

Prakhar1 — Thu, 25 Jul 2019 07:47:56 GMT

Hi All,

I am trying to pass an expression in the tMap using context variable. like this

But when I am passing it in the t Map to evaluate its Boolean value its always giving false as an output, whereas if i pass the same expression directly it is giving true for that.

Re: tMap Expression always return false when passing a string expression using context variable

lennelei — Thu, 25 Jul 2019 07:56:54 GMT

Hi,

first remark: context variables are linked to the job, not a component.

second remark: context variables are loaded at startup or with an tLoadContext component or explicitly assigned within the job (such as context.variable = value) (note that from my point of view, only the first use is recommanded).

That being said, what you are trying to do cannot work this way: values in the Context panel will not be evaluated as Java expression.

Could you please explain what exaclty you are trying to do?

Regards

Re: tMap Expression always return false when passing a string expression using context variable

Prakhar1 — Thu, 25 Jul 2019 08:05:46 GMT

I have a table containing the column names of the source table, and i want to take each column name and pass it in the expression. I will use java for this but i just tried it for one column but it's getting false output.

Re: tMap Expression always return false when passing a string expression using context variable

lennelei — Thu, 25 Jul 2019 08:18:03 GMT

Let's forgot the context part: why does the first column defined in your tMap doesn't work?

In your job, you have:

two db queries entering your tMap: what are they for?
no join between both that is to say that by default, you'll have a cross join (cartesian product of both queries) : that may give you a lot of rows!

row1.designation will have the different values of the input row: it seems to be what you want, doesn't it?

Re: tMap Expression always return false when passing a string expression using context variable

Prakhar1 — Thu, 25 Jul 2019 08:22:16 GMT

1) The first column works perfectly, but what will i do when i need to pass 100 columns in the same expression.

2) I forgot to join the 2 tables, but after that the same result is showing.

If this is not a good idea, can you tell me how to pass 100 different columns in the expression field in the same expression.

Re: tMap Expression always return false when passing a string expression using context variable

lennelei — Thu, 25 Jul 2019 08:54:47 GMT

Can't you use a tFlowToIterate to loop over your columns?

Re: tMap Expression always return false when passing a string expression using context variable

Prakhar1 — Thu, 25 Jul 2019 09:58:46 GMT

i haven't used it before

Re: tMap Expression always return false when passing a string expression using context variable

lennelei — Thu, 25 Jul 2019 10:15:31 GMT

It's never too late

One example:

tDBInput (read all columns) ==(row)==> tFlowToIterate ==(iterate)==> [ your process ]

This will run [ your process ] as many times as you have a row as input (100 times if you have 100 columns for example).

In [your process], you'll be able to use a globalMap variable from the tFlowToIterate to have the current column name.

You can see the documentation of the component here.

Re: tMap Expression always return false when passing a string expression using context variable

Prakhar1 — Thu, 25 Jul 2019 10:55:00 GMT

Thankyou for the guidance