org.litepal.crud

类 ClusterQuery

java.lang.Object

org.litepal.crud.ClusterQuery

public class ClusterQuery
extends java.lang.Object

Allows developers to query tables with cluster style.

从以下版本开始:

1.1

方法概要

限定符和类型	方法和说明
double	average(java.lang.Class<?> modelClass, java.lang.String column) Calculates the average value on a given column.
double	average(java.lang.String tableName, java.lang.String column) Calculates the average value on a given column.
int	count(java.lang.Class<?> modelClass) Count the records.
int	count(java.lang.String tableName) Count the records.
<T> java.util.List<T>	find(java.lang.Class<T> modelClass) Finds multiple records by the cluster parameters.
<T> java.util.List<T>	find(java.lang.Class<T> modelClass, boolean isEager) It is mostly same as find(Class) but an isEager parameter.
<T> T	findFirst(java.lang.Class<T> modelClass) Finds the first record by the cluster parameters.
<T> T	findFirst(java.lang.Class<T> modelClass, boolean isEager) It is mostly same as findFirst(Class) but an isEager parameter.
<T> T	findLast(java.lang.Class<T> modelClass) Finds the last record by the cluster parameters.
<T> T	findLast(java.lang.Class<T> modelClass, boolean isEager) It is mostly same as findLast(Class) but an isEager parameter.
ClusterQuery	limit(int value) Limits the number of rows returned by the query.
<T> T	max(java.lang.Class<?> modelClass, java.lang.String columnName, java.lang.Class<T> columnType) Calculates the maximum value on a given column.
<T> T	max(java.lang.String tableName, java.lang.String columnName, java.lang.Class<T> columnType) Calculates the maximum value on a given column.
<T> T	min(java.lang.Class<?> modelClass, java.lang.String columnName, java.lang.Class<T> columnType) Calculates the minimum value on a given column.
<T> T	min(java.lang.String tableName, java.lang.String columnName, java.lang.Class<T> columnType) Calculates the minimum value on a given column.
ClusterQuery	offset(int value) Declaring the offset of rows returned by the query.
ClusterQuery	order(java.lang.String column) Declaring how to order the rows queried from table.
ClusterQuery	select(java.lang.String... columns) Declaring to query which columns in table.
<T> T	sum(java.lang.Class<?> modelClass, java.lang.String columnName, java.lang.Class<T> columnType) Calculates the sum of values on a given column.
<T> T	sum(java.lang.String tableName, java.lang.String columnName, java.lang.Class<T> columnType) Calculates the sum of values on a given column.
ClusterQuery	where(java.lang.String... conditions) Declaring to query which rows in table.

从类继承的方法 java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

方法详细资料

select

public ClusterQuery select(java.lang.String... columns)

Declaring to query which columns in table.

 DataSupport.select("name", "age").find(Person.class);
 

This will find all rows with name and age columns in Person table.

参数:

columns - A String array of which columns to return. Passing null will return all columns.

返回:

A ClusterQuery instance.

where

public ClusterQuery where(java.lang.String... conditions)

Declaring to query which rows in table.

 DataSupport.where("name = ? or age > ?", "Tom", "14").find(Person.class);
 

This will find rows which name is Tom or age greater than 14 in Person table.

参数:

conditions - A filter declaring which rows to return, formatted as an SQL WHERE clause. Passing null will return all rows.

返回:

A ClusterQuery instance.

order

public ClusterQuery order(java.lang.String column)

Declaring how to order the rows queried from table.

 DataSupport.order("name desc").find(Person.class);
 

This will find all rows in Person table sorted by name with inverted order.

参数:

column - How to order the rows, formatted as an SQL ORDER BY clause. Passing null will use the default sort order, which may be unordered.

返回:

A ClusterQuery instance.

limit

public ClusterQuery limit(int value)

Limits the number of rows returned by the query.

 DataSupport.limit(2).find(Person.class);
 

This will find the top 2 rows in Person table.

参数:

value - Limits the number of rows returned by the query, formatted as LIMIT clause.

返回:

A ClusterQuery instance.

offset

public ClusterQuery offset(int value)

Declaring the offset of rows returned by the query. This method must be used with limit(int), or nothing will return.

 DataSupport.limit(1).offset(2).find(Person.class);
 

This will find the third row in Person table.

参数:

value - The offset amount of rows returned by the query.

返回:

A ClusterQuery instance.

find

public <T> java.util.List<T> find(java.lang.Class<T> modelClass)

Finds multiple records by the cluster parameters. You can use the below way to finish a complicated query:

 DataSupport.select("name").where("age > ?", "14").order("age").limit(1).offset(2)
                .find(Person.class);
 

You can also do the same job with SQLiteDatabase like this:

 getSQLiteDatabase().query("Person", "name", "age > ?", new String[] { "14" }, null, null, "age",
                "2,1");
 

Obviously, the first way is much more semantic.
Note that the associated models won't be loaded by default considering the efficiency, but you can do that by using find(Class, boolean).

参数:

modelClass - Which table to query and the object type to return as a list.

返回:

An object list with founded data from database, or an empty list.

find

public <T> java.util.List<T> find(java.lang.Class<T> modelClass,
                                  boolean isEager)

It is mostly same as find(Class) but an isEager parameter. If set true the associated models will be loaded as well.

参数:

modelClass - Which table to query and the object type to return as a list.

isEager - True to load the associated models, false not.

返回:

An object list with founded data from database, or an empty list.

findFirst

public <T> T findFirst(java.lang.Class<T> modelClass)

Finds the first record by the cluster parameters. You can use the below way to finish a complicated query:

 DataSupport.select("name").where("age > ?", "14").order("age").limit(1).offset(2)
                .findFirst(Person.class);
 

Note that the associated models won't be loaded by default considering the efficiency, but you can do that by using findFirst(Class, boolean).

参数:

modelClass - Which table to query and the object type to return.

返回:

An object with founded data from database, or null.

findFirst

public <T> T findFirst(java.lang.Class<T> modelClass,
                       boolean isEager)

It is mostly same as findFirst(Class) but an isEager parameter. If set true the associated models will be loaded as well.

参数:

modelClass - Which table to query and the object type to return.

isEager - True to load the associated models, false not.

返回:

An object with founded data from database, or null.

findLast

public <T> T findLast(java.lang.Class<T> modelClass)

Finds the last record by the cluster parameters. You can use the below way to finish a complicated query:

 DataSupport.select("name").where("age > ?", "14").order("age").limit(1).offset(2)
                .findLast(Person.class);
 

Note that the associated models won't be loaded by default considering the efficiency, but you can do that by using findLast(Class, boolean).

参数:

modelClass - Which table to query and the object type to return.

返回:

An object with founded data from database, or null.

findLast

public <T> T findLast(java.lang.Class<T> modelClass,
                      boolean isEager)

It is mostly same as findLast(Class) but an isEager parameter. If set true the associated models will be loaded as well.

参数:

modelClass - Which table to query and the object type to return.

isEager - True to load the associated models, false not.

返回:

An object with founded data from database, or null.

count

public int count(java.lang.Class<?> modelClass)

Count the records.

 DataSupport.count(Person.class);
 

This will count all rows in person table.
You can also specify a where clause when counting.

 DataSupport.where("age > ?", "15").count(Person.class);
 

参数:

modelClass - Which table to query from by class.

返回:

Count of the specified table.

count

public int count(java.lang.String tableName)

Count the records.

 DataSupport.count("person");
 

This will count all rows in person table.
You can also specify a where clause when counting.

 DataSupport.where("age > ?", "15").count("person");
 

参数:

tableName - Which table to query from.

返回:

Count of the specified table.

average

public double average(java.lang.Class<?> modelClass,
                      java.lang.String column)

Calculates the average value on a given column.

 DataSupport.average(Person.class, "age");
 

You can also specify a where clause when calculating.

 DataSupport.where("age > ?", "15").average(Person.class, "age");
 

参数:

modelClass - Which table to query from by class.

column - The based on column to calculate.

返回:

The average value on a given column.

average

public double average(java.lang.String tableName,
                      java.lang.String column)

Calculates the average value on a given column.

 DataSupport.average("person", "age");
 

You can also specify a where clause when calculating.

 DataSupport.where("age > ?", "15").average("person", "age");
 

参数:

tableName - Which table to query from.

column - The based on column to calculate.

返回:

The average value on a given column.

max

public <T> T max(java.lang.Class<?> modelClass,
                 java.lang.String columnName,
                 java.lang.Class<T> columnType)

Calculates the maximum value on a given column. The value is returned with the same data type of the column.

 DataSupport.max(Person.class, "age", int.class);
 

You can also specify a where clause when calculating.

 DataSupport.where("age > ?", "15").max(Person.class, "age", Integer.TYPE);
 

参数:

modelClass - Which table to query from by class.

columnName - The based on column to calculate.

columnType - The type of the based on column.

返回:

The maximum value on a given column.

max

public <T> T max(java.lang.String tableName,
                 java.lang.String columnName,
                 java.lang.Class<T> columnType)

Calculates the maximum value on a given column. The value is returned with the same data type of the column.

 DataSupport.max("person", "age", int.class);
 

You can also specify a where clause when calculating.

 DataSupport.where("age > ?", "15").max("person", "age", Integer.TYPE);
 

参数:

tableName - Which table to query from.

columnName - The based on column to calculate.

columnType - The type of the based on column.

返回:

The maximum value on a given column.

min

public <T> T min(java.lang.Class<?> modelClass,
                 java.lang.String columnName,
                 java.lang.Class<T> columnType)

Calculates the minimum value on a given column. The value is returned with the same data type of the column.

 DataSupport.min(Person.class, "age", int.class);
 

You can also specify a where clause when calculating.

 DataSupport.where("age > ?", "15").min(Person.class, "age", Integer.TYPE);
 

参数:

modelClass - Which table to query from by class.

columnName - The based on column to calculate.

columnType - The type of the based on column.

返回:

The minimum value on a given column.

min

public <T> T min(java.lang.String tableName,
                 java.lang.String columnName,
                 java.lang.Class<T> columnType)

Calculates the minimum value on a given column. The value is returned with the same data type of the column.

 DataSupport.min("person", "age", int.class);
 

You can also specify a where clause when calculating.

 DataSupport.where("age > ?", "15").min("person", "age", Integer.TYPE);
 

参数:

tableName - Which table to query from.

columnName - The based on column to calculate.

columnType - The type of the based on column.

返回:

The minimum value on a given column.

sum

public <T> T sum(java.lang.Class<?> modelClass,
                 java.lang.String columnName,
                 java.lang.Class<T> columnType)

Calculates the sum of values on a given column. The value is returned with the same data type of the column.

 DataSupport.sum(Person.class, "age", int.class);
 

You can also specify a where clause when calculating.

 DataSupport.where("age > ?", "15").sum(Person.class, "age", Integer.TYPE);
 

参数:

modelClass - Which table to query from by class.

columnName - The based on column to calculate.

columnType - The type of the based on column.

返回:

The sum value on a given column.

sum

public <T> T sum(java.lang.String tableName,
                 java.lang.String columnName,
                 java.lang.Class<T> columnType)

Calculates the sum of values on a given column. The value is returned with the same data type of the column.

 DataSupport.sum("person", "age", int.class);
 

You can also specify a where clause when calculating.

 DataSupport.where("age > ?", "15").sum("person", "age", Integer.TYPE);
 

参数:

tableName - Which table to query from.

columnName - The based on column to calculate.

columnType - The type of the based on column.

返回:

The sum value on a given column.