Reduce number of promises when rendering tree

We preload the first field of the first row if needed. This should ensure that
the following records are also loaded.
And we do not call load if the field is already loaded to avoid to create a
promise.

issue8199
review265411002

src/model.js

@@ -559,10 +559,13 @@
                 return jQuery.when.apply(jQuery, prms);
             }
         },
+        is_loaded: function(name) {
+            return ((this.id < 0) || (name in this._loaded));
+        },
         load: function(name) {
             var fname;
             var prm;
-            if ((this.id < 0) || (name in this._loaded)) {
+            if (this.is_loaded(name)) {
                 return jQuery.when();
             }
             if (this.group.prm.state() == 'pending') {

src/view/tree.js

@@ -806,21 +806,26 @@
     });
 
     function redraw_async(rows, selected, expanded) {
-        var chunk = Sao.config.display_size;
-        var dfd = jQuery.Deferred();
-        var redraw_rows = function(i) {
-            rows.slice(i, i + chunk).forEach(function(row) {
-                row.redraw(selected, expanded);
-            });
-            i += chunk;
-            if (i < rows.length) {
-                setTimeout(redraw_rows, 0, i);
-            } else {
-                dfd.resolve();
+        var dfd= jQuery.Deferred(),
+            i = 0;
+        var redraw = function() {
+            for (; i < rows.length; i++) {
+                var row = rows[i];
+                var record = row.record,
+                    column = row.tree.columns[0];
+                if (!record.is_loaded(column.attributes.name)) {
+                    // Prefetch the first field to prevent promises in
+                    // Cell.render
+                    record.load(column.attributes.name).done(redraw);
+                    return;
+                } else {
+                    row.redraw(selected, expanded);
+                }
             }
+            dfd.resolve();
         };
-        setTimeout(redraw_rows, 0, 0);
-        return dfd;
+        redraw();
+        return dfd.promise();
     }
 
     Sao.View.Tree.Row = Sao.class_(Object, {
@@ -1523,7 +1528,7 @@
             if (!cell) {
                 cell = this.get_cell();
             }
-            record.load(this.attributes.name).done(function() {
+            var render = function() {
                 var value;
                 var field = record.model.fields[this.attributes.name];
                 var invisible = field.get_state_attrs(record).invisible;
@@ -1574,7 +1579,12 @@
                     }
                     cell.text(value);
                 }
-            }.bind(this));
+            }.bind(this);
+            if (!record.is_loaded(this.attributes.name)) {
+                record.load(this.attributes.name).done(render);
+            } else {
+                render();
+            }
             return cell;
         },
         clicked: function(event) {
@@ -1610,7 +1620,7 @@
             if (!cell) {
                 cell = this.get_cell();
             }
-            record.load(this.attributes.name).done(function() {
+            var render = function() {
                 this.update_text(cell, record);
                 this.field.set_state(record);
                 var state_attrs = this.field.get_state_attrs(record);
@@ -1619,7 +1629,12 @@
                 } else {
                     cell.show();
                 }
-            }.bind(this));
+            }.bind(this);
+            if (!record.is_loaded(this.attributes.name)) {
+                record.load(this.attributes.name).done(render);
+            } else {
+                render();
+            }
             return cell;
         }
     });
@@ -1883,18 +1898,8 @@
             if (!cell) {
                 cell = this.get_cell();
             }
-            record.load(this.attributes.name).done(function() {
-                var value = this.field.get_client(record);
-                if (value) {
-                    if (value > Sao.common.BIG_IMAGE_SIZE) {
-                        value = jQuery.when(null);
-                    } else {
-                        value = this.field.get_data(record);
-                    }
-                } else {
-                    value = jQuery.when(null);
-                }
-                value.done(function(data) {
+            var render = function() {
+                var set_src = function(data) {
                     var img_url, blob;
                     if (!data) {
                         img_url = null;
@@ -1903,8 +1908,24 @@
                         img_url = window.URL.createObjectURL(blob);
                     }
                     cell.attr('src', img_url);
-                }.bind(this));
-            }.bind(this));
+                }.bind(this);
+
+                var value = this.field.get_client(record);
+                if (value) {
+                    if (value > Sao.common.BIG_IMAGE_SIZE) {
+                        set_src(null);
+                    } else {
+                        this.field.get_data(record).done(set_src);
+                    }
+                } else {
+                    set_src(null);
+                }
+            }.bind(this);
+            if (!record.is_loaded(this.attributes.name)) {
+                record.load(this.attributes.name).done(render);
+            } else {
+                render();
+            }
             return cell;
         }
     });
@@ -1975,10 +1996,7 @@
                         return undefined;
                     }
                 });
-            // Wait at least one eager field is loaded before evaluating states
-            record.load(fields[0]).done(function() {
-                button.set_state(record);
-            });
+            button.set_state(record);
             return button.el;
         },
         button_clicked: function(event) {