2.4Record traversal & file tables
The essentials in 30 seconds
- Traversal reviews the records of a file or a query; two approaches: the POUR TOUT loop (modern, recommended) and manual traversal (HLitPremier / HLitSuivant with an HEnDehors test).
- The Table control displays several records; the file table is linked to a file or a query and fills automatically, loading only the displayed rows.
- The memory table is filled by code (TableAjouteLigne): total freedom but loading to manage — reserve it for constructed data or controlled volumes.
Running mini-case — Yacine displays and traverses the product catalogue
Yacine, a WinDev developer at an SME trading electrical equipment in Oran, must display the product catalogue and identify those to restock. For the list shown on screen, he chooses a file table linked to a filtered query: it fills automatically and loads only the visible rows, even with thousands of references. To calculate stock alerts, he writes a traversal with the POUR TOUT Produit loop, concise and recommended, then adds the relevant lines to a second table. He takes care to also write the manual traversal (HLitPremier / HLitSuivant + HEnDehors test) to understand the underlying mechanism. Finally, he forbids himself from filling a memory table by traversing an entire large file: on large volumes, he prefers the file table with a filter and queries rather than a loop processing each record one by one.
Self-contained case for this section: it returns in the course, diagram, script and 48h challenge of section 2.4.
1. Two forms of traversal
After handling one record, you process sets. Traversal reviews the records of a file or a query. (1) The POUR TOUT loop: the modern and recommended form, concise and readable — it automatically traverses all records and handles the end of the traversal. (2) The manual loop with HLitPremier then HLitSuivant, testing HEnDehors to know when to stop: more verbose but essential to understand. In both cases, you can traverse according to an order (a key/index) and with a filter.
2. File table or memory table
The Table control is the natural companion of traversal: it displays several records in rows and columns. (1) The file table (known as “on file/query”) is linked to a data source and fills automatically; WinDev loads only the rows needed for display, which makes it performant even on very large volumes — the mode to favour in management applications. (2) The memory table is filled by code (TableAjouteLigne): total freedom but loading to manage — reserve it for constructed data or controlled volumes.
3. Performance vigilance
On large volumes, do not load everything into memory: prefer the file table with a filter. And for batch processing, favour queries or set-based functions rather than a loop processing a million records one by one. The classic trap — filling a memory table by traversing an entire large file — shows up mainly in production, when the real data arrives.
🔎 Concrete example — 🔎 Concrete example — POUR TOUT vs manual traversal
Two ways of writing the same traversal: Yacine identifies the products to restock.
// Recommended form: POUR TOUT
POUR TOUT Produit
SI Produit.Stock < 5 ALORS
TableAjouteLigne(TABLE_Alerte, Produit.CodeProduit, Produit.Stock)
FIN
FIN
// Manual form (understand the mechanism)
HLitPremier(Produit, hOrdreCroissant, "CodeProduit")
TANTQUE HEnDehors(Produit) = Faux
// ... process Produit ...
HLitSuivant(Produit)
FIN
Reading : POUR TOUT handles progression and the end; the manual form shows the mechanism
Reflex : FILE table for display, do not load everything into memoryReading: POUR TOUT traverses all records and stops by itself; manual traversal makes HLitPremier / HLitSuivant and the HEnDehors test explicit.
Lesson: for display, prefer a file table linked to a query rather than loading everything into memory.
Section vocabulary
- Traversal
- Reviewing the records of a file or a query, possibly according to an order (a key) and with a filter.
Simple example: Yacine traverses the Produit file to identify low stock.
What it is not: reading a single record identified by its key.
Reflex: process a set of records → a traversal.
- POUR TOUT
- The modern and recommended form of traversal: concise, readable, it automatically manages progression and the end of the traversal.
Simple example: Yacine writes POUR TOUT Produit to calculate alerts.
What it is not: a manual loop with HLitPremier / HLitSuivant.
Reflex: simple and readable traversal → POUR TOUT.
- Manual traversal
- The classic form: HLitPremier then HLitSuivant, testing HEnDehors to detect the end.
Simple example: Yacine writes the manual version to understand the mechanism.
What it is not: the POUR TOUT loop, which hides these steps.
Reflex: see what really happens → manual traversal.
- File table
- A table control linked directly to a file or a query: automatic filling, WinDev loads only the displayed rows.
Simple example: Yacine displays his catalogue in a file table based on a query.
What it is not: a table filled line by line by code.
Reflex: display large volumes → file table.
- Memory table
- A table control filled by code (TableAjouteLigne): total freedom but loading to manage yourself.
Simple example: Yacine fills a memory table with only the products in alert.
What it is not: a table linked to a database query.
Reflex: data constructed by code → memory table.
In practice — In practice — Traversing and displaying records
- Write a traversal with POUR TOUT (recommended form) to process all the records of a file or a query, like Yacine.
- Write the same traversal in manual form (HLitPremier / HLitSuivant + HEnDehors test) to understand the underlying mechanism.
- For display, preferably use a file table linked to a file or a query: it fills automatically and remains performant on large volumes.
- Reserve the memory table (TableAjouteLigne) for data constructed by code, and on large volumes filter rather than loading everything.
Step-by-step script — traverse the catalogue like Yacine (5 min)
1) Create a file table linked to a filtered Produit query (stock < threshold). 2) Write a POUR TOUT Produit traversal that tests Produit.Stock. 3) Add the products in alert to a memory table via TableAjouteLigne. 4) Rewrite the traversal in manual form (HLitPremier / HLitSuivant + HEnDehors) to analyse it. 5) On a large volume, check that you are not loading everything into memory.
Default reflex in management applications: as soon as the data comes from the database, use a file table based on a query.
Copy-paste template — my traversal & my table
POUR TOUT traversal: POUR TOUT Produit ... FIN (recommended)
Manual traversal : HLitPremier(...) ; TANTQUE HEnDehors(...) = Faux ... HLitSuivant(...) ; FIN
FILE table : linked to a file/query, AUTO fill, displayed rows
MEMORY table : filled by CODE (TableAjouteLigne)
Rules : (1) display from database -> FILE table
(2) large batch processing -> QUERIES, not a row-by-row loopPOUR TOUT traversal
Yacine traverses the whole Produit file to recalculate stock alerts.
Manual traversal
Yacine writes the HLitPremier / HLitSuivant version to understand the flow.
File table
Yacine displays the catalogue via a table linked to a query, loaded on demand.
Memory table
Yacine fills a small table of only the out-of-stock products by code.
✓ Best practices
- Use POUR TOUT by default, and know manual traversal.
- Display database data with a file table linked to a query.
- Do not load everything into memory on large volumes.
✗ Common pitfalls
- Filling a memory table by traversing a large file.
- Believing that a file table cannot be sorted.
- Processing a million records one by one rather than with a query.
Key takeaways
- Two forms of traversal: POUR TOUT (recommended) and manual traversal (HLitPremier / HLitSuivant + HEnDehors).
- The Table control displays records; the file table is linked to a file/query and loads only the displayed rows.
- The memory table is filled by code (TableAjouteLigne) — reserve it for constructed data.
- On large volumes: file table + filter; batch processing via queries.
48h challenge — apply it tomorrow
Like Yacine, write a POUR TOUT traversal on a file in your application, then rewrite it in manual form (HLitPremier / HLitSuivant + HEnDehors test). Then display that data in a file table linked to a query and check that it loads only the visible rows. Explain in one sentence why you must not fill a memory table by traversing an entire large file.
- I know how to write a traversal with POUR TOUT and in manual form.
- I choose between file table and memory table according to the origin and volume of the data.
- I know how not to load everything into memory on large volumes.
Frequently asked questions
What is the difference between a file table and a memory table?
The file table is linked to a file or a query and loads only the displayed rows: it is performant even on very large volumes. The memory table is filled by code and loads everything into memory: total freedom but unsuitable for large volumes. In management applications, the file table is therefore preferred.
Why learn manual traversal when POUR TOUT exists?
Because it shows what really happens (moving from one record to the next, testing the end) and remains useful in special cases. POUR TOUT is the modern and recommended form for everyday use; understanding manual traversal helps diagnose tricky situations.
What is the difference between a file table and a memory table?