fix(core): Fix float custom field handling

Closes #1561. This change ensures that default float values in MySQL do not get rounded at all, and
also leaves other drivers alone so that spurious migrations are not created for postgres.

packages/core/e2e/custom-fields.e2e-spec.ts

@@ -28,7 +28,7 @@ const customConfig = mergeConfig(testConfig(), {
             { name: 'stringWithDefault', type: 'string', defaultValue: 'hello' },
             { name: 'localeStringWithDefault', type: 'localeString', defaultValue: 'hola' },
             { name: 'intWithDefault', type: 'int', defaultValue: 5 },
-            { name: 'floatWithDefault', type: 'float', defaultValue: 5.5 },
+            { name: 'floatWithDefault', type: 'float', defaultValue: 5.5678 },
             { name: 'booleanWithDefault', type: 'boolean', defaultValue: true },
             {
                 name: 'dateTimeWithDefault',
@@ -324,7 +324,7 @@ describe('Custom fields', () => {
             stringWithDefault: 'hello',
             localeStringWithDefault: 'hola',
             intWithDefault: 5,
-            floatWithDefault: 5.5,
+            floatWithDefault: 5.5678,
             booleanWithDefault: true,
             dateTimeWithDefault: '2019-04-30T12:59:16.415Z',
             // MySQL does not support defaults on TEXT fields, which is what "simple-json" uses

packages/core/src/entity/register-custom-entity-fields.ts

@@ -101,8 +101,17 @@ function registerCustomFieldsForEntity(
                         }
                         options.length = length;
                     }
-                    if (customField.type === 'float') {
-                        options.scale = 2;
+                    if (
+                        customField.type === 'float' &&
+                        typeof customField.defaultValue === 'number' &&
+                        (dbEngine === 'mariadb' || dbEngine === 'mysql')
+                    ) {
+                        // In the MySQL driver, a default float value will get rounded to the nearest integer.
+                        // unless you specify the precision.
+                        const defaultValueDecimalPlaces = customField.defaultValue.toString().split('.')[1];
+                        if (defaultValueDecimalPlaces) {
+                            options.precision = defaultValueDecimalPlaces.length;
+                        }
                     }
                     if (
                         customField.type === 'datetime' &&