EasyCursor

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Language
Java
Version
v1.0.0 (Jul 24, 2015)
Created
Mar 28, 2014
Updated
Nov 12, 2017
Owner
Alexandros Schillings (alt236)
Contributor
Alexandros Schillings (alt236)
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EasyCursor

For those who find statements like cursor.getString(cursor.getColumnIndexOrThrow(COLUMN_NAME)); or cursor.getColumnIndex(COLUMN)==-1 ? value=FALLBACK : value=cursor.getString(COLUMN); a bit too arcane and verbose.

Also, for those that have to maintain both a CursorAdaptor and an ArrayAdaptor for the same data from different sources.

There are 3 types of EasyCursors:

  1. EasySqlCursor - A wrapper for normal SqlCursors
  2. EasyJsonCursor (experimental) - Converts a JSONArray into a Cursor
  3. EasyObjectCursor (experimental) - Converts a List/Array of generic Objects into a Cursor.

EasyCursors in general offer the following benefits:

  1. A number of code simplification functions such as cursor.getString(COLUMN_NAME) to reduce verbosity.
  2. A way of accessing optional columns/fields such as cursor.optLong(COLUMN_NAME) and cursor.optLong(COLUMN_NAME, FALLBACK_VALUE).
  3. (Optionally) A way to store the way the cursor was constructed so that it can be stored for later re-creation. Currently the library only implements this for the EasySqlCursor but it can be build for the others as well.

EasySqlCursors also offer:

  1. A way to access booleans directly (i.e. cursor.getBoolean()/ cursor.optBoolean()). The default implementation of EasySqlCursor is defined in DefaultBooleanLogic.java and assumes that true==1 and false!=1 where 1 is a number, but it can be changed by passing a custom BooleanLogic implementation in the constructor.

Getting Started Guide

Including the Library in Your Project

This project is available as an artifact for use with Gradle. To use that, add the following blocks to your build.gradle file:

 repositories {
  maven {
   url "https://dl.bintray.com/alt236/maven"
  }
 }

 dependencies {
  compile 'uk.co.alt236:easycursor-android:1.0.0'
 }

If you really need a Jar file, fork the project and execute ./gradlew clean build generateRelease at the root of the project. This will create a zip file under <PROJECT_ROOT>/library/build/ the Jar can be found inside.

EasySqlCursors

This is the way to convert boring old cursors to an EasyCursor:

final Cursor cursor = builder.query(...);
    
cursor.moveToFirst();
    
final EasyCursor eCursor = new EasySqlCursor(cursor);

Notes and Caveats:

  • Look here for a more in-depth explanation on how EasySqlCursors work.

EasyJsonCursors

Any JSON array can be converted to a cursor like this:

  final JSONArray jArray = ... // Any Json Array.

  // If the JSONObjects in the JSONArray do not have an android-valid "_id" field,
  // you can setup an alias.
  final String _idAlias = "id"; 
  final EasyCursor cursor = new EasyJsonCursor(jArray, _idAlias);

Notes and Caveats:

  • The "columns" array for the "getColumnIndexOrThrow() / getColumnIndex()" methods is calculated based on the JSON fields of the first array item. This means that if the other items have more, you will not be able to access them using any of the getXXX methods - you will get an IllegalArgumentException. To access those fields you will need to use the optXXX methods.

  • EasyJsonCursor is internally using org.json. Normally, org.json getXXX methods throw checked JsonExceptions but in order to keep the EasyCursor API consistent these exceptions are caught (when thrown from getXXX methods) and re-thrown as runtime IllegalArgumentExceptions or ConversionErrorExceptions.

  • getBytes()/optBytes() is not implemented and will throw an UnsupportedOperationException when called.

  • In addition to the usual EasyCursor methods, an EasyJsonCursor also has the following:

    1. getJsonObject(String name)
    2. getJsonArray(String name)
    3. optJsonObject(String name)
    4. optJsonArray(String name)

EasyObjectCursors

  final List<WhateverObject> data = ... // somehow get an object list

  // If the Objects in the list do not have "get_Id()" getter method, 
  // you can setup an alias. The alias below will match a "getId()" method.
  final String _idAlias = "id"; 
  final EasyCursor cursor = new EasyObjectCursor<WhateverObject>(WhateverObject.class, data, _idAlias);

Notes and Caveats:

  • The "columns" array for the "getColumnIndexOrThrow() / getColumnIndex()" methods is calculated as follows:

    • Take the class type you passed as a parameter in the constructor
    • Reflectively get all public methods with zero parameters which are non-void and their name is more than 3 characters long.
    • Check to see if they start with "get" or "is".
    • If they do, chop the "get" / "is" prefix off, lowercase them add add them to the array.
    • This means that if you call cursor.getBytes("mymethod") you will internally call thegetMyMethod()` getter of the current object.
  • In addition to the usual EasyCursor methods, an EasyObjectCursor also has the following:

    1. getItem() - Which returns the current object.
    2. getObject(int fieldNo) - Which return the result of the getter execution as an object
    3. getObject(String name) - Which return the result of the getter execution as an object
    4. optObject(int fieldNo) - Which return the result of the getter execution as an object
    5. optObject(String name) - Which return the result of the getter execution as an object
  • An EasyObjectCursor will not catch any exceptions that calling an object's method will throw.

  • When calling a get[Number] or /opt[Number] method the following actions will take place:

    1. Check to see if what comes out of the getter is an instance of the Number class. If so, return the correct type
    2. If not, check if the object is a String and try to parse it as the requested Number type
    3. Throw a ConversionErrorException
  • The getBlob() / getBlob() methods is only valid for the types listed below. Any other will throw a ConversionErrorException.

    1. Strings
    2. ByteArrays
    3. Integers
    4. Long
    5. Float
    6. Double
    7. Short

 

EasySqlCursors In Depth

Creation

1. Using one of the included Builders EasyQueryModel

This is the "native" way of using EasyCursor.

For a normal Select Query:

  final SqlQueryModel model = new SqlQueryModel.SelectQueryBuilder()
    .setDistinct(true)
    .setProjectionIn("track.trackId AS _id", "artist.name AS artist", "album.title AS album", "mediatype.name AS media")
    .setTables("track LEFT OUTER JOIN album ON track.albumId = album.albumid")
    .setSelection("media=?")
    .setSelectionArgs("MPEG audio file")
    .setSortOrder("artist, album, track, composer")
    .setModelComment("Example query")
    .build();
    
  final EasyCursor eCursor = model.execute(db.getReadableDatabase());

For a raw SQL query:

  private static final String RAW_QUERY =
    "SELECT track.trackId AS _id, artist.name AS artist, album.title AS album, track.name AS track, mediatype.name AS media, track.composer AS composer, (ifnull(track.composer, 0)>0) AS hascomposer, SUM(track.Milliseconds) AS meaninglessSum, SUM(track.Milliseconds)/3.33 AS meaninglessDiv"
    + " FROM track"
    + " LEFT OUTER JOIN album ON track.albumId = album.albumid"
    + " LEFT OUTER JOIN artist ON artist.artistId = album.artistid"
    + " LEFT OUTER JOIN mediatype ON track.mediatypeid = mediatype.mediatypeid"
    + " WHERE media=?"
    + " GROUP BY album"
    + " HAVING SUM(track.Milliseconds) > 1000"
    + " ORDER BY artist, album, track, composer"
    + " LIMIT 10000";
              
  final SqlQueryModel model = new SqlQueryModel.RawQueryBuilder()
    .setRawSql(RAW_QUERY)
    .setSelectionArgs("MPEG audio file")
    .setModelComment("Raw query")
    .build();

  final EasyCursor eCursor = model.execute(db.getReadableDatabase());

2. Using an QueryBuilder Interface

You can define a class implementing either the SqlSelectBuilder or SqlRawQueryBuilder interfaces and do the following: This way you can write, or re-use, your own builders. The following example reads a little bit more like a "standard" SQL statement:

  final LousyQueryBuilder builder = new LousyQueryBuilder();

  final SqlQueryModel model = builder
      .setSelect("track.trackId AS _id", "artist.name AS artist", "album.title AS album", "mediatype.name AS media")
      .setFrom("track LEFT OUTER JOIN album ON track.albumId = album.albumid")
      .setWhere("media=?")
      .setWhereArgs("MPEG audio file")
      .setOrderBy("artist, album, track, composer")
      .build();
    
  model.setComment("Builder query");
      
  final EasyCursor eCursor = model.execute(db.getReadableDatabase());

3. The Backwards Compatible way

You can convert an existing Cursor to an EasyCursor by wrapping it like this:

  // Android build-in query builder.
  final SQLiteQueryBuilder builder = new SQLiteQueryBuilder();

  builder.setTables("track LEFT OUTER JOIN album ON track.albumId = album.albumid");
  builder.setDistinct(true);

  final Cursor cursor = builder.query(
    getReadableDatabase(),
    "track.trackId AS _id", "artist.name AS artist", "album.title AS album", "mediatype.name AS media",
    "media=?",
    "MPEG audio file",
    null,
    null,
    "artist, album, track, composer");

  cursor.moveToFirst();

  final EasyCursor eCursor = new EasySqlCursor(cursor);

But, as you did not use an SqlQueryModel, you will not be able to access the JSON representation of the query.

4. The "Compatibility" way

By compatibility I mean that the API is similar to a SQLiteQueryBuilder.

  final EasyCompatSqlModelBuilder builder = new EasyCompatSqlModelBuilder();

  builder.setTables(QueryConstants.DEFAULT_TABLES);
  builder.setDistinct(true);
  builder.setQueryParams(
    "track.trackId AS _id", "artist.name AS artist", "album.title AS album", "mediatype.name AS media",
    "media=?",
    "MPEG audio file",
    null,
    null,
    "artist, album, track, composer");

  final SqlQueryModel model = builder.build();

  model.setModelComment("Default compat query");

  final EasyCursor eCursor = model.execute(getReadableDatabase());

The setQueryParams() method has an identical signature to SQLiteQueryBuilder.query() minus the database instance parameter.

Things you can do with an EasyCursor

An EasyCursor offers (apart from the usual Cursor methods) the following:

  • easycursor.getXXX(String columnName) : Which is shorthand for easycursor.getXXX(easycursor.getColumnIndexOrThrow(COLUMN_NAME)).
  • easycursor.optXXX(String columnName) : Which will return an implementation specific fallback value if the column is missing (see the Javadoc for details).
  • easycursor.optXXX(String columnName, XXX fallback): Which will return the provided fallback value if the column is missing.
  • easycursor.optXXXAsWrapperType(String columnName): Which will return null if the column is missing ( if anyone can think of a better name let me know :)).

Where XXX is the usual data types (long, int, String, etc.).

Not all functions are available for all datatypes though, as some are meaningless ( getStringAsWrapperType() for example).

Booleans

In addition you get the following functions for booleans, which work the same as the ones above:

  • easycursor.getBoolean(String columnName)
  • easycursor.optBoolean(String columnName)
  • easycursor.optBoolean(String columnName, boolean fallback)
  • easycursor.optBooleanAsWrapperType(String columnName)

The logic behind a boolean is as follows: true==1 and false!=1 is defined in DefaultBooleanLogic.java.

Accessing an EasyCursor's EasyQueryModel, saving it and replaying

If the cursor has been generated via an EasyQueryModel, then you can access the model like this:

  final SqlQueryModel model = easycursor.getQueryModel()`

The model can then be converted to a JSON string via its model.toJson() function.

To re-create the model, you can do the following:

  final SqlQueryModel model = SqlJsonModelConverter.convert(jsonString);

The following snippet will get the Model JSON of a cursor, save it in local prefs, read it back and re-query:

  // Get the JSON of a cursor model
  final String jsonOut = oldCursor.getQueryModel().toJson();

  // Store it in local prefs
  final SharedPreferences settings = PreferenceManager.getDefaultSharedPreferences(this);
  final SharedPreferences.Editor editor = settings.edit();
  editor.putString(Constants.PREFS_SAVED_QUERY, jsonOut);
  editor.commit();

  // Read it back
  final String jsonIn = settings.getString(Constants.PREFS_SAVED_QUERY, null);

  // Recreate the model and execute the query
  final SqlQueryModel model = SqlJsonModelConverter.convert(jsonString);
  final EasyCursor eCursor = model.execute(getReadableDatabase());

Keeping track of an EasyQueryModel

In order to keep track of an EasyQueryModel file and help in maintaining compatibility of the model to the underlying DB (if your schema can change), you can use the following functions.

  • setModelComment(String comment)/String getModelComment()
  • setModelTag(String tag)/ String getModelTag()
  • setModelVersion(int version)/ int getModelVersion()

There is no business logic behind these functions -- it is up to each user to keep a compatibility matrix.

Extending the implementation of EasySqlCursor

If you need to extend the base implementation of EasySqlCursor, for example because you treat booleans differently, you can use the following syntax:

final EasyCursor cursor = model.execute(getReadableDatabase(), MyExtendedEasyCursor.class);

Things to remember

  1. An EasyCursor directly extends the default Cursor interface, so you can pass it around as a standard Cursor.
  2. When using an SqlQueryModel, the resulting Cursor is automatically moved to the first position.
  3. When you call execute() on an SqlQueryModel it still internally uses a standard Android SQLiteQueryBuilder, which will throw any usual exceptions.
  4. When you call execute() on an SqlQueryModel the execution happens on the same thread it was called in.

Changelog

  • v0.1.0 First public release
  • v0.1.1 Fixed a crash caused by not properly handing null arrays in JsonPayloadHelper
  • v1.0.0 API tidy, proper release.

Links

Credits

Author: Alexandros Schillings.

The code in this project is licensed under the Apache Software License 2.0.

Copyright (c) 2017 Alexandros Schillings.