fix(storage): 修正 Database 上 get 方法对不含 where 字段 query 的处理

...并在 concat selector 时进行的查询信息等价比较上，妥善处理
predicateProvider 为空而导致没有 toString 方法可调用，throw 的情况。

...resolves #93

src/storage/Database.ts

@@ -445,7 +445,7 @@ export class Database {
         mainTable: table!
       }
       const { limit, skip } = clause
-      const provider = new PredicateProvider(table!, clause.where!)
+      const provider = clause.where ? new PredicateProvider(table!, clause.where) : null
 
       return new Selector<T>(db, query, matcher, provider, limit, skip, orderDesc)
     })

src/storage/modules/Selector.ts

@@ -201,12 +201,19 @@ export class Selector <T> {
 
   concat(... selectors: Selector<T>[]): Selector<T> {
     const orderStr = Selector.stringifyOrder(this.orderDescriptions!)
-    const equal = selectors.every(m =>
-      m.select === this.select &&
-      m.predicateProvider!.toString() === this.predicateProvider!.toString() &&
-      Selector.stringifyOrder(m.orderDescriptions!) === orderStr &&
-      m.mapFn.toString() === this.mapFn.toString()
-    )
+    const equal = selectors.every(m => {
+      const hasEqualPredProvider =
+        m.predicateProvider == null && this.predicateProvider == null
+        || (
+          m.predicateProvider && this.predicateProvider
+          && m.predicateProvider.toString() === this.predicateProvider.toString()
+        )
+
+      return !!hasEqualPredProvider
+        && m.select === this.select
+        && Selector.stringifyOrder(m.orderDescriptions!) === orderStr
+        && m.mapFn.toString() === this.mapFn.toString()
+    })
     assert(equal, Exception.TokenConcatFailed())
 
     return Selector.concatFactory(this, ...selectors)
@@ -236,19 +243,27 @@ export class Selector <T> {
   }
 
   private getQuery(additional?: lf.Predicate): lf.query.Select {
-    if (this.predicateBuildErr && !additional) {
-      return this.query
+    if (this.predicateBuildErr) {
+      return additional ? this.query.where(additional) : this.query
     }
-    // !this.predicateBuildErr || additional
+    // !this.predicateBuildErr
+
     const preds: lf.Predicate[] = []
-    if (this.predicateProvider && !this.predicateBuildErr) {
+    if (this.predicateProvider) {
       preds.push(this.predicateProvider.getPredicate()!)
     }
     if (additional) {
       preds.push(additional)
     }
-    const pred = lf.op.and(...preds)
-    return this.query.where(pred)
+
+    switch (preds.length) {
+      case 0:
+        return this.query
+      case 1:
+        return this.query.where(preds[0])
+      default:
+        return this.query.where(lf.op.and(...preds))
+    }
   }
 
   private removeKey(data: any[], key: string) {

test/specs/storage/Database.public.spec.ts

@@ -1,4 +1,4 @@
-import { Observable } from 'rxjs/Observable'
+import { Observable, Scheduler } from 'rxjs'
 import * as moment from 'moment'
 import { describe, it, beforeEach, afterEach } from 'tman'
 import { expect, assert, use } from 'chai'
@@ -10,7 +10,7 @@ import { TestFixture2 } from '../../schemas/Test'
 import { scenarioGen, programGen, postGen, taskGen, subtaskGen } from '../../utils/generators'
 import { RDBType, DataStoreType, Database, clone, forEach, JoinMode } from '../../index'
 import { TaskSchema, ProjectSchema, PostSchema, ModuleSchema, ProgramSchema, SubtaskSchema } from '../../index'
-import { InvalidQuery, NonExistentTable, InvalidType, PrimaryKeyNotProvided, NotConnected } from '../../index'
+import { InvalidQuery, NonExistentTable, InvalidType, PrimaryKeyNotProvided, NotConnected, Selector } from '../../index'
 
 use(SinonChai)
 
@@ -251,6 +251,15 @@ export default describe('Database Testcase: ', () => {
       expect(_projectId).to.equal(target._projectId)
     })
 
+    it('on query without `where`, should result in QueryToken whose Selector does not have predicateProvider', function* () {
+      yield database.get<TaskSchema>('Task', {}).selector$
+        .subscribeOn(Scheduler.async)
+        .do((x: Selector<TaskSchema>) => {
+          console.info(x.toString())
+          expect(x.predicateProvider).to.be.null
+        })
+    })
+
     it('should get single record successfully', function* () {
       const result = yield database.get<TaskSchema>('Task', {
         where: { _id: target._id }

test/specs/storage/modules/Selector.spec.ts

@@ -153,7 +153,7 @@ export default describe('Selector test', () => {
 
     const sql = selector.toString()
 
-    expect(sql).to.equal('SELECT * FROM TestSelectMetadata WHERE ((TestSelectMetadata.time > 50));')
+    expect(sql).to.equal('SELECT * FROM TestSelectMetadata WHERE (TestSelectMetadata.time > 50);')
   })
 
   it('should get correct results with orderBy', function* () {
@@ -922,6 +922,26 @@ export default describe('Selector test', () => {
         .do(r => expect(r[75].name).equal(update3))
     })
 
+    it('concat selector should ok when neither selectors have predicateProvider', function* () {
+      selector1 = new Selector(db,
+        db.select().from(table),
+        tableShape,
+        null,
+        20, 0
+      )
+      selector2 = new Selector(db,
+        db.select().from(table),
+        tableShape,
+        null,
+        20, 20
+      )
+      const result = yield selector1.concat(selector2).values()
+      expect(result).to.have.lengthOf(40)
+      result.forEach((r: any, index: number) => {
+        expect(r).to.deep.equal(storeData[index])
+      })
+    })
+
     it('concat selector should ok with OrderDescription', function* () {
       const selector6 = new Selector(db,
         db.select().from(table),