diff --git a/src/db.ts b/src/db.ts
index 2b1f409..2bab005 100644
--- a/src/db.ts
+++ b/src/db.ts
@@ -7,7 +7,7 @@ import ChangelogModel from './models/changelog';
 // database urls, prod db url is retrieved automatically
 const TESTING_URL = 'mongodb://localhost/dfopdb_test';
 const DEV_URL = 'mongodb://localhost/dfopdb';
-const debugging = false;
+const debugging = true;
 
 if (process.env.NODE_ENV !== 'production' && debugging) {
   mongoose.set('debug', true);  // enable mongoose debug
diff --git a/src/routes/sample.ts b/src/routes/sample.ts
index f3395c8..ef87ab3 100644
--- a/src/routes/sample.ts
+++ b/src/routes/sample.ts
@@ -43,6 +43,54 @@ router.get('/samples', async (req, res, next) => {
   if (!filters['to-page']) {  // set to-page default
     filters['to-page'] = 0;
   }
+  const addedFilter = filters.filters.find(e => e.field === 'added');
+  if (addedFilter) {  // convert added filter to object id
+    filters.filters.splice(filters.filters.findIndex(e => e.field === 'added'), 1);
+    if (addedFilter.mode === 'in') {
+      const v = [];  // query value
+      addedFilter.values.forEach(value => {
+        const date = [new Date(value).setHours(0,0,0,0), new Date(value).setHours(23,59,59,999)];
+        v.push({$and: [{ _id: { '$gte': dateToOId(date[0])}}, { _id: { '$lte': dateToOId(date[1])}}]});
+      });
+      filters.filters.push({mode: 'or', field: '_id', values: v});
+    }
+    else if (addedFilter.mode === 'nin') {
+      addedFilter.values = addedFilter.values.sort();
+      const v = [];  // query value
+
+      for (let i = 0; i <= addedFilter.values.length; i ++) {
+        v[i] = {$and: []};
+        if (i > 0) {
+          const date = new Date(addedFilter.values[i - 1]).setHours(23,59,59,999);
+          v[i].$and.push({ _id: { '$gt': dateToOId(date)}}) ;
+        }
+        if (i < addedFilter.values.length) {
+          const date = new Date(addedFilter.values[i]).setHours(0,0,0,0);
+          v[i].$and.push({ _id: { '$lt': dateToOId(date)}}) ;
+        }
+      }
+      filters.filters.push({mode: 'or', field: '_id', values: v});
+    }
+    else {
+      // start and end of day
+      const date = [new Date(addedFilter.values[0]).setHours(0,0,0,0), new Date(addedFilter.values[0]).setHours(23,59,59,999)];
+      if (addedFilter.mode === 'lt') {  // lt start
+        filters.filters.push({mode: 'lt', field: '_id', values: [dateToOId(date[0])]});
+      }
+      if (addedFilter.mode === 'eq' || addedFilter.mode === 'lte') {  // lte end
+        filters.filters.push({mode: 'lte', field: '_id', values: [dateToOId(date[1])]});
+      }
+      if (addedFilter.mode === 'gt') {  // gt end
+        filters.filters.push({mode: 'gt', field: '_id', values: [dateToOId(date[1])]});
+      }
+      if (addedFilter.mode === 'eq' || addedFilter.mode === 'gte') {  // gte start
+        filters.filters.push({mode: 'gte', field: '_id', values: [dateToOId(date[0])]});
+      }
+      if (addedFilter.mode === 'ne') {
+        filters.filters.push({mode: 'or', field: '_id', values: [{ _id: { '$lt': dateToOId(date[0])}}, { _id: { '$gt': dateToOId(date[1])}}]});
+      }
+    }
+  }
 
   const sortFilterKeys = filters.filters.map(e => e.field);
 
@@ -80,7 +128,6 @@ router.get('/samples', async (req, res, next) => {
       {$addFields: {['sample.' + measurementName]: '$measurement.values'}},  // more restructuring
       {$replaceRoot: {newRoot: {$mergeObjects: [{$arrayElemAt: ['$sample', 0]}, {}]}}}
     );
-    addFilterQueries(queryPtr, filters.filters.filter(e => sampleKeys.indexOf(e.field) >= 0));  // sample filters
   }
   else {  // sorting with samples as starting collection
     collection = SampleModel;
@@ -568,13 +615,23 @@ module.exports = router;
 
 async function numberGenerate (sample, req, res, next) {  // generate number in format Location32, returns false on error
   const sampleData = await SampleModel
-    .findOne({number: new RegExp('^' + req.authDetails.location + '[0-9]+$', 'm')})
-    .sort({number: -1})
-    .lean()
+    // .findOne({number: new RegExp('^' + req.authDetails.location + '[0-9]+$', 'm')})
+    // .sort({number: -1})
+    // .lean()
+    .aggregate([
+      {$match: {number: new RegExp('^' + 'Rng' + '[0-9]+$', 'm')}},
+      // {$addFields: {number2: {$toDecimal: {$arrayElemAt: [{$split: [{$arrayElemAt: [{$split: ['$number', 'Rng']}, 1]}, '_']}, 0]}}}},  // not working with MongoDb 3.6
+      {$addFields: {sortNumber: {$let: {
+        vars: {tmp: {$concat: ['000000000000000000000000000000', {$arrayElemAt: [{$split: [{$arrayElemAt: [{$split: ['$number', 'Rng']}, 1]}, '_']}, 0]}]}},
+        in: {$substrCP: ['$$tmp', {$subtract: [{$strLenCP: '$$tmp'}, 30]}, {$strLenCP: '$$tmp'}]}
+      }}}},
+      {$sort: {sortNumber: -1}},
+      {$limit: 1}
+    ])
     .exec()
     .catch(err => next(err));
   if (sampleData instanceof Error) return false;
-  return req.authDetails.location + (sampleData ? Number(sampleData.number.replace(/[^0-9]+/g, '')) + 1 : 1);
+  return req.authDetails.location + (sampleData[0] ? Number(sampleData[0].number.replace(/[^0-9]+/g, '')) + 1 : 1);
 }
 
 async function numberCheck(sample, res, next) {
@@ -707,5 +764,16 @@ function addFilterQueries (queryPtr, filters) {  // returns array of match queri
 }
 
 function filterQueries (filters) {
-  return filters.map(e => ({[e.field]: {['$' + e.mode]: (e.mode.indexOf('in') >= 0 ? e.values : e.values[0])}}))  // add filter criteria as {field: {$mode: value}}, only use first value when mode is not in/nin
+  return filters.map(e => {
+    if (e.mode === 'or') {  // allow or queries (needed for $ne added)
+      return {['$' + e.mode]: e.values};
+    }
+    else {
+      return {[e.field]: {['$' + e.mode]: (e.mode.indexOf('in') >= 0 ? e.values : e.values[0])}};  // add filter criteria as {field: {$mode: value}}, only use first value when mode is not in/nin
+    }
+  });
+}
+
+function dateToOId (date) {  // convert date to ObjectId
+  return mongoose.Types.ObjectId(Math.floor(date / 1000).toString(16) + '0000000000000000');
 }
\ No newline at end of file
diff --git a/src/routes/validate/sample.ts b/src/routes/validate/sample.ts
index f84a5be..ef0fa0a 100644
--- a/src/routes/validate/sample.ts
+++ b/src/routes/validate/sample.ts
@@ -175,7 +175,7 @@ export default class SampleValidate {
             let validator;
             let field = data.filters[i].field
             if (/material\./.test(field)) {  // select right validation model
-              validator = MaterialValidate.outputV();
+              validator = MaterialValidate.outputV().append({number: Joi.string().max(128).allow('')});
               field = field.replace('material.', '');
             }
             else if (/measurements\./.test(field)) {
@@ -195,7 +195,7 @@ export default class SampleValidate {
               validator = Joi.object(this.sample);
             }
             const {value, error} = validator.validate({[field]: e});
-            if (error) throw error;  // reject invalid values
+            if (error) throw error;  // reject invalid values  // TODO: return exact error description, handle in frontend filters
             return value[field];
           });
         }
@@ -215,7 +215,7 @@ export default class SampleValidate {
       filters: Joi.array().items(Joi.object({
         mode: Joi.string().valid('eq', 'ne', 'lt', 'lte', 'gt', 'gte', 'in', 'nin'),
         field: Joi.string().pattern(new RegExp('^(' + this.fieldKeys.join('|').replace(/\./g, '\\.').replace(/\*/g, '.+') + ')$', 'm')),
-        values: Joi.array().items(Joi.alternatives().try(Joi.string().max(128), Joi.number(), Joi.boolean())).min(1)
+        values: Joi.array().items(Joi.alternatives().try(Joi.string().max(128), Joi.number(), Joi.boolean(), Joi.date().iso())).min(1)
       })).default([])
     }).with('to-page', 'page-size').validate(data);
   }