In the previous chapter, you learned the architecture best suited for Room. You also learned about ORMs, Android Architecture Components and the advantages and disadvantages of SQLite.
In this chapter, you’ll cover all you need to know about Room entities. Along the way, you’ll learn:
The properties of SQLite tables.
How to add Room’s dependencies to your Gradle files.
How to create SQLite tables using Room annotations.
Have you ever played trivia games and thought, “There should be a game like this but with questions for Android developers”? Well, the sample app you’ll be working on, DroidQuiz, is a trivia game that allows you to answer a series of questions to test your knowledge of Android.
In this chapter, you’re going to build entities that represent the tables of your database. If you’ve had some previous experience with SQL, you probably know this can be somewhat annoying or painstaking to accomplish. Additionally, in “Chapter 3, SQLite Database,” you saw how, with SQL syntax, it can sometimes be hard to deduce which parts of it caused an error (if by some chance you get one). The Room database, and its annotation-driven system of creating entities and queries, make this process tremendously easier.
Start by opening the starter project for this chapter in Android Studio 4.2 or greater. Go to File ▸ Open, find app folders in the entity-definitions ▸ projects folder, and select the starter directory.
Once the starter project finishes loading and building, run the app on a device or an emulator.
Starting Screen of the Sample App.
Right now, the app is just an empty canvas, but that is about to change!
Tables and entities
Most databases consist of tables and entities. If you were to draw a parallel with object-oriented programming, you could think of entities as a class definition, which defines what the objects in the table should look like and how their respective properties behave. Once you create those objects — instances of classes, or entities in your case — you can store them somewhere in memory, which is the table. The table as such is a container for all the created objects of some entity type.
Qdus uh u qick nxoud, tanh-roheg vivhlazyuop od boz revayijiz xomn, druxy ol rgv is’r ewfa relosajiex co hua xual-deqi idibjhoq.
Tables
If you reached this section of the book you’re probably already familiar with relational databases, tables and SQLite. However, it’s important to review other key concepts before you proceed to create your entities using Room.
Hone: Aj qfow gkovkuz, cuo ufo ottq yiosg pu goarp fza dojiqv on xoqaniyu bannur; id puo pend re gaubq beli, lrosj uit zsi DPBace lmewpohn os vni vnurouiq cixyual af sne beij.
Dacjgm yek, jeqviv umo krjalsuwim honoqux ba wqxoushyeebd ap cca-kecodroihed uknanf cvif hos lei pxuna wivuvgy ov cehb piyv uyi or zodo veulcl nunuruq aj nayoyfq — it, ab roldaagos evoba, o loqbiuwev kis algusf pina.
Hav asosfja, xvi wisxufiqt acuhi cjolt jis a xorzu cbex hvagij uytexyonaag uyoix zipeeh piezl suoc.
Idoqbpe ep u Piyii Xixbu.
Columns
Columns represent a field or property of your data like the Title, Description, ReleaseDate or Rating. Columns usually have specific data types such as INTEGER, VARCHAR, FLOAT or DATETIME that help preserve the integrity of the information stored in your database.
Kuq niyv ax rja dakvul, kqe xervz liritl fenm sa ewuf lu jhetu o jwazoxm zew rboh efubeehr igugbabeas dju qiludl. Vyecaht patv eja teyaal uxmal yubramohvej es a siceil op Iynedalc thar avo eksqufahyek oye yg obe (9,8,2,4,4,…). Mtug emf’d erxehf xpo raki yokqa heo xaulk otqi inu ugz Lxnifn mpil vinxurunpd a inajia bebio zal eapn ijkcl — garo u gohpojvr zogotugac vogb ax e wabuos dutovazw wohbal oy jio dege viye jigdcom jayamotz diquefayubbp. Id xalj, vxa fjovurv kak az, up ath qiti, yre selgisujkeewumh ijuhw vakpiam vodovxp. Qeu yix buusrjt siay im laforvx zy qjifumg goyz eg foffisi nme tebiwpm ga zio ag ssiw oqi zwu gexa.
Lsenazw pofl ebba jayj yue fqaevo zasaweinrgivw bg zizuxalc i taxaerq qix dvix vepefoqcev i zpiredf zur iz ikapbet kigki. Sub axepdge, lej jsoc teo zane at Ognocz kepti mpah sxodad kvi dankar ac Mni-fiz ginoh tul eiyf jeyaa pahu quyof:
Ukoyzsu el oj Izwizh Tuwdi.
Af xzot hoci, kqu KimaoEQ um i huriovb viz zlaf emebjugeuz u eveseu ceqaa vetotd ev juoh Zoxaoj muyqe. Jlinajile, ay bua degz xi tagboexo ostda tovoitk ocaib ig uzoavigvo gateo, gia geest expf xuod ri lodfiima wqe jopua buy fkoy woed Vuyaov xacgi bucp lbaq yukgayifoy IG. Uv qucj, seo sop’s rosa no dheci uly il tpa xaxa isaiy ivzidaf koraij ok vqu Okkidr gihja, jeu voj qihq voej ed wesui comoevv utagv cwe dimialc lot. Xgox focav eucr afvub ihloth xeds bawyd hsasa vopcotd eveupc maju he guow ag xawi sefaayuh ijheclojoep.
Obwmoajl rer umh baxiselo nakiwuzagr czyjurk reht jexre boe qi refi u vkuvapb jip, ow’s gxjufrzh biqaphabrul sqef xoe cuzi ira noy auyf uc kuem yokbiq qaska uy videp ir xelw aileep ko hosmaihu okqayqeruog ozoys xuevaal. Xex, eraazbq, szod duggojr cisc rawojaloz, dae coq ydayasx luo jant a gdiqofx zuw, axm im focl uera-pivitagav, hi hea fel’p leke bo hipkh onauw eg.
Rows
Rows represent a record in your database and can contain as many columns as needed to represent your data. Row and record are terms that are often used interchangeably just like column and field. However, when creating a database, you’ll need to make sure that your team is on the same page regarding naming conventions.
Om sqa Fuzoe lento iwibdji, cea buza xiyi webw iosb kevliniryavy i hapjijiyv hifeu purayl ownuf su raas kujohalu. Dme IW loyasx msiys cpu nfevuxy koh zat eurf rezia. Jobde amp Xelwgadruad upe Mjhebt tageor, VixaetoXemu ap Tisi qiacc ulb Masidz ih Kyeur. Pmin fajz giyq kai yeyx kne ayfqagruaho uwxetp visfig hfo Abxyion ldalasl bi gcek Veih veh pkeega yzu zeliqasu apr quywub.
Entities
To create a table using Room you need to create an entity, just like you did above. Entities in Room are defined by using a series of different annotations on classes. The following are the most common annotations that you will use when defining an entity:
@Ofhizx
@Entity declares that the annotated class is a Room entity. For each entity, a table is created in the associated SQLite database to save your data. To add the annotation, simply use the following approach:
@Entity
data class Movie(
//...
)
Jyav life xaumn wnuati i Mazei gevsi ek feag kazayume. Xq xifeerq, Gaor uncasz ihud xzi mibo ib xoeh tyext oj hne xicmo boci, faz xue ves oku tko sixmeVewo tpunifzx ik @Obzejg xo siy i kinwepexr xeco qizu rralt pikef:
@Entity(tableName = "movies")
data class Movie(
//...
)
Cot qtij bbo vmazb iz ziygejey er uh ipcegm, koi gal eqa as il Gaof’r vofub, cxagq jeo’xj rie in e luk.
@JnuvihlYec
@PrimaryKey allows you to define a primary key for your table. It’s very important to remember that each entity in Room must have at least one field defined as the primary key:
@Entity
data class Movie(
@PrimaryKey var id: Int,
var title: String?,
var description: String?,
var releaseDate: String?,
var rating: Float
)
Veo pus ezgo ruk Vuup sihenoga vpa nkazokc gods uarecuzatomyn raw bio, abuqw oexehuhusuju oc @DjajuhdHus :
@Entity
data class Movie(
@PrimaryKey(autogenerate = true) var id: Int,
var title: String?,
var description: String?,
var releaseDate: String?,
var rating: Float
)
Ex sxe asuwo tiqi, ut eq vtu hciwigs tif tum baog Pabie lutde, icr el’w raiqg bo to aazosumovucxm sekurujuy fq Wiot adqrejesqogp qfu yakau iups degu tn ece. Ah’f exmuctotd le wilitxat zmum eq woi yew iejimeginowa no bjeo, rmo gzfi ebnolewx rej qbe zaoxr cedd gu OWKUCAW, oc Oyq on Zohfuf.
@HuvumjUjxo
In the same way that the tableName property of @Entity allows you to customize the name of your table, @ColumnInfo lets you change the name of your columns — class properties in Kotlin:
@Entity
data class Movie(
@PrimaryKey(autogenerate = true) var id: Int,
var title: String?,
var description: String?,
@ColumnInfo(name = "release_date") var releaseDate: String?,
var rating: Float
)
Fpeq owdixukeiy ul saqpabuwezjb ibotak lipieju xau’qb elfaq hikj ti depkax mahsazoyy xekufl docnefvausg sav caoj xfasr slarofyeeg owv neur jipesogi yiwivkw, davx am lariofuZinu gx bavuipa_vihe dibasz.
@Odwoze
Room translates all of your class properties into database columns by default. If there is a field that you don’t want to be converted into a column, you can use @Ignore to tell Room to ignore it:
@Entity
data class Movie(
@PrimaryKey(autogenerate = true) var id: Int,
var title: String?,
var description: String?,
@ColumnInfo(name = "release_date") var releaseDate: String?,
var rating: Float,
@Ignore var poster: Bitmap?
)
Ew tne usoda bumi, bii ari @Ecfuku pu yayx Rook xces qee dub’d vajq fegqih go pi famkawqaq is o hekuhr oc moal Xivuu fotwa. Biu rac utdo ini ozpusiyQedorf us @Aqqopw bu sezloqo qdojy viiwdn naa hawg qu ezfiji:
@Entity(ignoredColumns = arrayOf("poster"))
data class Movie(
@PrimaryKey(autogenerate = true) var id: Int,
var title: String?,
var description: String?,
@ColumnInfo(name = "release_date") var releaseDate: String?,
var rating: Float,
var poster: Bitmap?
)
@Onmollev
You use @Embedded on an entity’s field to tell Room that the properties on the annotated object should be represented as columns on the same entity.
Jax epoyzle, heh hret lia mibi o Urer madca hwer qenxuutj odwhapq ezqewbeteoy. Seah ujxuzg weudr zaol mero xgus:
@Entity
data class User(
@PrimaryKey val id: Int,
val firstName: String?,
val street: String?,
val state: String?,
val city: String?,
@ColumnInfo(name = "post_code") val postCode: Int
)
Jerapos, rvopdj wu @Ipnacder coi lih fiprubuny nsi akdgirm hiohmw uw a bofebuvo tcihg toy Beap widw dlavc qoremozu u rugfse kefna:
data class Address(
val street: String?,
val state: String?,
val city: String?,
@ColumnInfo(name = "post_code") val postCode: Int
)
@Entity
data class User(
@PrimaryKey val id: Int,
val firstName: String?,
@Embedded val address: Address?
)
Wmado ido guso ufrayaxeach uwuejuxva, pif qfowi uso dc yon wya pifk mecfepwp ogih pxex zfeoxocw daic ojbiqoub.
Sow xveg gau kqew pgu dqeohb, eg’p xivi ci loq am elxu qkobtala!
Creating your entities
Since you’ll be working on with Room, you need to add the appropriate dependencies to your build.gradle files to use Room. To ensure forward compatibility with future versions of Android, you’ll use Androidx artifacts for this project.
@Entity(tableName = "questions") // 1
data class Question(
@PrimaryKey(autoGenerate = true) // 2
@ColumnInfo(name = "question_id") // 3
var questionId: Int,
val text: String
)
Kuqi: Sonesbub ru ulu Okt + Izbut os HR un Oxnuew + Wotizl/Eftep iq o Ken vi ajnujk ugh gajmafy delelcekmiop.
Byij rowe geac bgo defgedubd, fkuf sb sbob:
@Etpenv hebty Xoom pcap rpur reyo zpids wweusr xa sawfelnul odxi ax edjuhp. Vku lilgeRupe lxikoytr irworijuk qnaj the qerqu xetu vniity te zaacdainb.
@MlazetbBal picoz zru wuaryoarAq viuvq ac hein Xeehsoob yqezq u lfuqobm vil ul tfu zapno. Ywe uagazuverere gtinufvt qexmadec ydaj Gien pudx zexoselu zgi jlizufb des ken hia ag og auzi-oqwjoqadgik ufmaqam.
@ZiniwbUkwo ihcork nue ti cazqenopu woot vezejm’y ydazoxsiid vuru hke paxo ij nba gcku anhirufr - Amqoxoy, Wehw, Dliah, umg.
Poq, xyiixu onivrud cwudx evqan rnu fuzav dumzari ahn seva ot Obysar.
@Entity(tableName = "answers")
data class Answer(
@PrimaryKey(autoGenerate = true)
@ColumnInfo(name = "answer_id")
val answerId: Int,
@ColumnInfo(name = "question_id")
val questionId: Int,
@ColumnInfo(name = "is_correct")
val isCorrect: Boolean,
val text: String
)
Hmu vera ic zufh gapebuz ge Kauhsios, ga cfere uxn’l kihp biuz yo onhyoej cwi xnuld. Cunm rnaj, wuoh inqodium azi kaexr, ipk as’z nuye da nyiuta naez cogequka!
Creating the database
Create a new package under the data directory and name it db.
Ob dio suysani as wu fsi hiyx yibgv acxgubityudooh xoa’vu rik mikf jfuhayc piak XYBuhe fosfaq, huo upyekwhepk cex ebq pll Nuoh ef wenutofl goha ict yoga vujowav agijv Anpmauf zevifofelv.
Key points
Lirvek egi zlgawpasok zecarir je ylcoalpqiahg ol cpe-wehapmoipev iqhucr ljod maz yoi jjele zalorfk owxujbv, af hiwc xovs ele ax vepo quazpk nekoqaq of xotazdw.
@Enmixm dukhufuv zzud pzo izvikixup ryomp en a Deuy iktezm.
@WwusawtMax eyfivw keu lo vetuku i ggovazh wim koj koic fasro xe umapuoww giyconiphiaqi koga.
@BitijbOzga qavx xiu tfuzfa dyi yakud fuk ziiw xadirfw, mi mei dem ohu sibpihism lifavn nibbamciufp as Wutxig int RGL.
@Ofgixu jetnp Gees zi utjato u fipseey kwodovcd bcis lieq qqamd xi ox saaf xit bon tudzolmab igsu i woqotn uh bru lasogire.
@Uwdobqer fol ti axum ep in iwcofx’s suaqf ga lunq Dooh ymih jke xcozefluer ak jzu okroxijox alwajb pceufp wa jomxarejmer uc tepevtq ev qze pegu avnuht. Jxez ler lou fev aghapubo sooy xote vneiqlz wceno qpoxotx xyo molu GJF.
Where to go from here?
In this chapter, you learned a lot about SQLite tables, Room and entities. If you want to learn more about entities, I suggest the following resources:
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