Why computed column has to be string?

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Posted on by Community Member

Hi all,

Anyone can give me some understanding why computed column should always be a string ?

Noted in Microsoft Docs also specify this, but I just want to know the reason for this ?

https://docs.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/data-entities/data-entity-computed-columns-virtual-fields#properties-of-unmapped-fields

Thanks,

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Gunjan Bhattachayya 35,423 on at

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Hi,

The computed column is not always string. It could be Int, Int64, Real, Enum etc.

The computed field data method, however, should return a string value as it is CAST into the desired data type. The method is converted into TSQL as per the link you provided.

You can check SalesInvoiceHeaderV2Entiity\TotalDiscountAmount field as an example of a computed field of data type Real.

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Jeremy_Mounet 170 on at

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Hello

As Gujan said, computed columns are not always a string. It contains the "result" of a computed columns "method", this one bound on the view by a property of the computed field.

On the other hand, the computed column method should return always a string because the result of its return during synchronization process, will be the SQL code part to execute for the column on the global SQL query of the view. A computed column method is also not something to code for a X++ execution but something to write SQL expression (by using SysComputed class framework for instance).

For this kind of object and for training, I suggest to edit in SQL some views with computed columns with SSMS to see the result of the synchronization.

Hope it helps.

Jérémy.

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nmaenpaa 101,160 Moderator on at

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The computed column definition must be a string because it must return a T-SQL statement that is then executed to populate the values to the actual computed column.

Unlike display methods, which contain code and return some value, the computed column x++ definition returns "code" (T-SQL) statement. The x++ code is executed in db sync, unlike a display method which is executed during runtime. In computed columns the T-SQL statement is the code that is executed during runtime (in the database).

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Joris dG 17,775 on at

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What Nikolaos said. It's important to understand the computed column's _method_ will NEVER execute when the view is used. It's executed ONCE when the database sync runs, and its output goes straight into the SQL view's statement. It is not dynamic... The string you produce will be executed in SQL every time the view executes.

I blogged about this many years ago when this feature was introduced in AX2012. This information is still accurate: daxmusings.codecrib.com/.../computed-view-columns-in-ax-2012.html

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Faisal Fareed 10,796 User Group Leader on at

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I myself learnt about computed columns many years ago from this link daxmusings.codecrib.com/.../computed-view-columns-in-ax-2012.html and I confirm this is still valid - very well explained.

I also documented my understanding here https://daxture.blogspot.com/2015/03/computed-columns-in-views-dynamics-ax.html

However, read through MS docs article too to get initial understand and understand comparisons.

docs.microsoft.com/.../data-entity-computed-columns-virtual-fields

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Community Member on at

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Thank you all for your kind explanation.

Much appreciated.

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