Migration
migration
migration=========================== 如何写migration ========================= 1.migration的结构每⼀个migrate的类都是 ActiveRecord::Migration 的⼦类,每⼀个migrate都要重写两个⽅法 up 和 down:Ruby代码1. class CreateProducts < ActiveRecord::Migration2. def self.up3. #想⼲嘛,就⼲嘛4. end5. def self.down6. #你后悔的时候,你会怎么做?7. end8. end简单的说 up ⽅法就是操作数据库时⽤的,down就是你后悔了,⽤来回滚⽤的.2.migration提供调⽤的⽅法Migrations提供了⼀系列的⽅法来操作数据库:Ruby代码1. create_table #建表2. change_table #修改表结构3. drop_table #删除表4. add_column #增加字段5. change_column #修改字段定义6. rename_column #修改字段名7. remove_column #删除字段8. add_index #创建索引9. remove_index #删除索引Ruby代码1. execute <<-SQL2. ALTER TABLE products ADD CONSTRAINT fk_products_categories FOREIGN KEY (category_id) REFERENCES categories(id)3. SQL3.字段定义字段有两种⽅法:Ruby代码1. #这个是传统的⽅法2. create_table :products do |t|3. t.column :name, :string, :null => false4. end5.6. #这个刚出来的时候,⼤家都说很性感,其实不外乎就是定义⼀系列的快捷⽅法: string,7. # text, integer, float, decimal, datetime, timestamp, time, date,8. # binary, boolean . 这⼀系列的⽅法对应各种数据类型,9. # 还有 primary_key ⽅法是⽤来定义主键的.10. create_table :products do |t|11. t.string :name12. end除了这⼏个经典的定义字段⽅法外,还有两个特别的Helper⽅法:Ruby代码1. #以下这个⽅法会⾃动在表中增加 created_at,updated_at这两个类型为timestamp的字段2. change_table :products do |t|3. t.timestamps4. end5.6. #这个⽅法是定义关于关系的,但是不会为你的表加上外键约束,如果你加上约束,请另外⼿动添加,切记!7. create_table :products do |t|8. t.references :category# ⽣成 category_id9.10. #这个是关联关系中多态的定义,⽣成两个字段 attachment_id 和 attachment_type ,并且attachment_type的默认值为 'Photo'11. t.references :attachment, :polymorphic => {:default => 'Photo'}12. end以上两个⽅法是锦上添花之作,相当的实⽤.4.在migration中使⽤ Model除了使⽤以上⽅法操作数据库外,其实还可以直接在migration中使⽤ Model 的.⽐如:Ruby代码1. def self.up2. #直接就⽤model来更新数据库,3. #你可以看到 migration ⼀直在提供便利让你避免使⽤SQL,当然不是说SQL不好,只是想让你更加的统⼀,只要ruby就好了.4. User.update_all ["receive_newsletter = ?", true]5. end使⽤model的另外⼀种情况是:当前migration要删除表中的⼀个字段 first_name,但是你的model中的某个⽅法使⽤了这个字段作为验证,⽐如:Ruby代码1. class User < ActiveRecord::Base2. validates_presence_of :first_name3. end那么当你要在migration中增加⼀条记录时,这个验证便不能通过,如:Ruby代码1. def self.up2. User.create({:name => 'name'}).save3. end在这种情况下,你可以在migration中重新定义⼀个model:Ruby代码1. class XXXMigration < ActiveRecord::Migration2. class User < ActiveRecord::Base3. end4. def self.up5. remove_column :first_name6. end7.8. #这个⽅法的作⽤就是取得最新的表定义9. User.reset_column_information10. #放⼼吧,这个User不会有 validates_presence_of :first_name 的验证11. User.create({:name => 'name'}).save=========================== migration⽂件的命名 ======================= 按照Migration的约定去命名你的migration⽂件,会令你省不少功夫的,请千万要相信这⼀点. 如果migration⽂件名是这样的格式: AddXXXToYYY” or “RemoveXXXFromYYY XXX => 字段名, YYY => 表名. 那么migration⽣成的时候,Rails会⾃动为你加上 add_column or remove_column ⽐如:Ruby代码1. #留意类名2. class AddPartNumberToProducts < ActiveRecord::Migration3. def self.up4. add_column :products, :part_number, :string5. end6. def self.down7. remove_column :products, :part_number8. end9. end10.11. class RemovePartNumberFromProducts < ActiveRecord::Migration12. def self.up13. remove_column :products, :part_number14. end15. def self.down16. add_column :products, :part_number, :string17. end18. endcool吧??=========================== 如何执⾏migration ========================= 执⾏migration的经典⽅法:Ruby代码1. rake db:migrate2.3. #执⾏特定版本4. rake db:migrate VERSION=200809061200001、创建数据库表格在创建Model后，Rails ⾃动的在/db/migrate⽂件夹中⽣成了迁移编号_create_Model名.rb 格式的⽂件，如006_create_users.rb打开该⽂件，做如下修改class CreateUsers < ActiveRecord::Migrationdef self.up#此处加⼊要创建的表格create_table "users" do |t|t.column :login, :string, :null => falset.column :email, :stringt.column :crypted_password, :string, :limit => 40 # 字符长度限制t.column :salt, :string, :limit => 40t.column :created_at, :datetimet.column :updated_at, :datetimet.column :remember_token, :stringt.column :remember_token_expires_at, :datetimet.column :flag, :boolean, :null => false, :default => false #设置默认值endenddef self.downdrop_table "users"endend保存后，运⾏rake db:migration这样就可以在config/database.yml ⽂件⾥配置的数据库中创建⼀个名为：users的数据库表，并且拥有相应的表字段。
Migration
288
AEA PAPERS AND PROCEEDINGS
MAY 1999
-P\
ity is ambiguous. However, where capital, risk, or human-capital constraints bind, these impacts are not likely to be zero as in the case of a perfect-markets, separable agricultural household model (e.g., I. Singh et al., 1986). The finding of a significant impact of migration or remittances on productivity would be evidence in support of the new economics of migration. Positive impacts would suggest that migration complements productivity growth in the farm sector by relaxing credit or risk constraints, while negative impacts would suggest that increased migration exacerbates labor shortages. Few tests of this NELM hypothesis have appeared in the literature; exceptions include Robert B. B. Lucas (1987) and Taylor (1992). Dwayne Benjamin and Loren Brandt (1998) find evidence that participation in migration loosens risk constraints on household-farm investments. If migrants play the role of financial intermediaries, as these studies suggest, the ex ante incentive to participate in migration may be large. However, households' propensity to encourage members to migrate may be mitigated when there are other ways to finance farm investments or if the loss of labor to migration canies a high cost in temis of forgone yields. n. Methods If production is constrained and migration, M, and remittances, /?. are important in shaping production constraints, constrained yield response, y*', depends on A/and ^ . ' The core equation of our model is;^ (2) K^ = y,, +
animal migration阅读理解
一、动物迁徙的定义动物迁徙是指动物为了寻找食物、繁殖或逃避恶劣环境而进行的周期性或不定期的长距离移动。
这种行为在世界各地的动物种裙中都很常见，例如鸟类、鱼类、哺乳动物和昆虫等都有迁徙的现象。
二、动物迁徙的原因1. 寻找食物：一些动物在特定季节内会随着季节的变化前往其他地区寻找更丰富的食物资源。
例如北极燕鸥会在冬季从北极飞往南方地区，以寻找更多的捕食机会。
2. 繁殖：很多动物为了繁殖会进行迁徙，他们会选择适合繁殖的环境，比如鸟类会选择气候温暖、食物丰富的地方来进行繁殖。
3. 逃避恶劣环境：一些动物会在气候恶劣或资源匮乏的环境下进行迁徙，以找到更适合生存的地方。
比如北极熊会在夏季融冰时离开北极圈附近的海域，而在冬季再返回那里。
三、动物迁徙的影响1. 生态平衡：动物迁徙对生态系统的平衡有着重要的影响，它可以帮助不同地区的生态系统之间实现资源的平衡，避免某一地区资源过度捕食，同时也有利于种裙的繁衍生息。
2. 保护物种多样性：动物迁徙可以促进物种之间的交流和繁衍，有利于物种的多样性和繁荣。
同时也对一些动植物保护区的管理提出了挑战，需要保护区之间进行有效的连接。
3. 经济影响：一些动物迁徙对人类的经济生活也有一定的影响，比如渔民依靠鱼类迁徙的路线进行捕捞，如果鱼类迁徙的路线发生改变，会给渔业带来不利影响。
四、动物迁徙的保护与管理因为动物迁徙对生态系统的重要性，对动物迁徙的保护和管理也变得尤为重要。
1. 跨国合作：很多动物会跨越多个国家的边界进行迁徙，因此需要各国间加强合作，共同保护迁徙动物的栖息地。
2. 制定保护政策：各国需要制定相应的保护政策，通过保护区的划定和管理，保护迁徙动物的迁徙路线。
3. 科学研究：加强对迁徙动物的科学研究，了解它们的迁徙规律和重要迁徙地，为制定有效的保护措施提供科学依据。
五、结语动物迁徙是自然界一项惊人的现象，它不仅是生物多样性的表现，同时也对生态系统的平衡具有重要影响。
为了保护动物迁徙的现象，我们需要加强全球合作，制定有效的保护政策，保护好每一个迁徙动物的迁徙之路。
migration是什么意思
migration是什么意思migration英[ magren ]美[ maɡren ]TOEFL /n.迁移移居变形复数：migrations友谊的小船说翻就翻？No！我要不翻的shi~~选择要添加的生词本新建生词本进入生词本每日一句发现频道双语例句权威例句1.The scale of migration took a quantum lea in the early 1970s. 20世纪70年代初移民的规模骤然扩大。
2.During the last recession, migration to the sunbelt accelerated.在上个经济萧条期人们向美国南部阳光地带移民的速度加快了。
3.Birthlace data are only the crudest indicator of actual migration aths.出生地信息只能非常粗略地显示实际移民过程。
查看更多1.This migration is creating a fresh set of tensions.来自BBC2.We'll be sying in on his migration south.来自BBC3.Only migration kees oulation growing in the develoed world.来自SA查看更多柯林斯高阶英汉双解学习词典1VERB移居迁徙(尤指到外地寻找工作或暂住一段时间)If eole migrate, they move from one lace to another,esecially in order to find work or to live somewhere for a short time.eole migrate to cities like Jakarta in search of work...人们为找工作而迁移到雅加达这类城市里。
2012年英语二翻译加重点词
2012When people in developing countries worry about migration,they are usually concerned at the prospect of their best and brightest departure to Silicon Vall ey or to hospitals and universities in the developed world .当发展中国家人们为移民问题焦虑的时候，他们通常是在担忧他们的民族里那些最优秀最聪明的人的前景，这些人去了硅谷或者发达国家的医院和高校重点词汇：migration [maɪ'greɪʃ(ə)n] n.移民迁移| concern at 对...关注| prospect 前景| brightest 最优秀的最聪明的| depart v.离开动身出发departure 离开动身出发These are the kind of workers that countries like Britain ,Canada and Australia try to attract b y using immigration rules that privilege college graduates 。
这些就是那种像英国、加拿大、澳大利亚等国家通过使用赋予大学生特权的移民法规所试图吸引的人重点词汇：privilege n.特权v.赋予…特权Lots of studies have found that well-educated people from developing countries are particular ly likely to emigrate .许多研究也发现，发展中国家的受过良好教育的人尤其可能会移民重点词汇：emigrate[‘emɪgreɪt] 移居外国移民（到国外）immigrate['ɪmɪgreɪt]移民（到国内）使移居入境A big survey of Indian households in 2004 found that nearly 40%of emigrants had more than a high-school education, compared with around 3.3% of all Indians over the age of 25.在2004年的印度家庭的一个大规模调查中发现，接近40%的移民受过高中以上的教育，与之形成鲜明对比的是，所有超过25岁的印度人中只有大概3.3%的人受过高中以上的教育重点词汇：household n.家庭adj.家庭的|This "brain drain "has long bothered policymakers in poor countries ,They fear that it hurts th eir economies ,depriving them of much-needed skilled workers who could have taught at thei r universities ,worked in their hospitals and come up with clever new products for their factor ies to make 。
migration
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10. Paris
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Miami
Miami is a global city in southeastern Florida, in the United States. Nickname(s): The Magic City ,the best known city in Florida. Miami is ranked as a global city for its importance in finance, commerce, media, entertainment, arts and international trade.
民的,移居的
Definition
移植, 随季节而移居, (鸟类的)迁徙 ①move from one country or region to another and settle there ②move periodically or seasonall immigrate [‘imigreit] v.移居入境 ① To enter and settle in a country or region to which one is not native.
Toronto
The largest city in Canada and is the provincial capital of Ontario . It is located on the north-western shore of Lake Ontario. Toronto is a clean, safe city with a wonderful network of parks, recreational, and cultural facilities. One of the world's most ethnically diverse cities, it is home to more than 80 ethnic communities from Africa, Asia, and Europe. Toronto is also the business centre of Canada.
migrate词根
词根migr-migrate：['maɪɡret] v.（使）移居；（使）迁移；（使）迁徙结构分析：migrate=migr（迁移，移居）+ate（动词后缀）→（使）迁移，（使）移居migration：[maɪˈɡreɪʃn]n. 迁移；移居；移民【超纲】结构分析：migration=migrat(e)（迁移，移居）+ion（名词后缀）→迁移，移居migratory：[ˈmaɪɡrətɔːri]adj. 迁移的；迁徙的【超纲】结构分析：migratory=migrat(e)（迁移，移居）+ory（形容词后缀）→迁移的，迁徙的migrant：[ˈmaɪɡrənt]n.（为工作）移居者，流动季节工；候鸟adj.迁移的，移居的【超纲】结构分析：migrant=migr（迁移，移居）+ant（形容词后缀）→迁移的，移居的（人）immigrate：[ˈɪmɪɡreɪt]vi.迁移进入vt.使迁移入境【超纲】结构分析：immigrate=im（=in，进入）+migr（迁移，移居）+ate（动词后缀）→迁移进入immigration：[,ɪmɪ'ɡreʃən] n.迁移入境结构分析：immigration=immigrat(e)（迁移进入）+ion（名词后缀）→迁移入境immigratory：['ɪməgrə,tɔri]adj. 迁入的；迁移入境的【超纲】结构分析：immigratory=immigrat(e)（迁移进入）+ory（形容词后缀）→迁移入境的immigrant：['ɪmɪɡrənt] adj. 移民的；迁入的n. 移民，侨民结构分析：immigrant=im（=in，进入）+migr（迁移）+ant（形容词后缀）→迁入的，移民的（人）emigrate：['ɛmɪɡret]v.移民出境；移居外国结构分析：emigrate=e（=ex，出去）+migr（迁移）+ate（动词后缀）→迁移出去→移民出境，移居外国emigration：[ˌemɪˈɡreɪʃn]n.移民出境；移居外国【超纲】结构分析：emigration=emigrat(e)（迁移出去）+ion（名词后缀）→移民出境，移居外国emigratory：['emiɡrətəri]adj. 移民出境的；移居外国的【超纲】结构分析：emigratory=emigrat(e)（迁移出去）+ory（形容词后缀）→移民出境的，移居外国的emigrant：['ɛmɪɡrənt]n.移民出境者；侨民adj.移民出境的；移居的【超纲】结构分析：emigrant=e（=ex，出去）+migr（迁移）+ant（形容词后缀）→移民出境的（人）→移民出境者，侨民。
迁移抑制率公式 mir mathtype 英语
迁移抑制率（Migration Inhibition Rate）通常用于评估某种药物或化合物对细胞迁移能力的影响。
在实验中，研究人员会比较处理组（添加了药物或化合物的样本）和对照组（未添加药物或化合物的样本）的细胞迁移情况。
迁移抑制率的计算公式如下：Migration Inhibition Rate (\%) = [(Control Migration - Treated Migration) / Control Migration] × 100其中：- Control Migration：对照组的细胞迁移距离或数量。
- Treated Migration：处理组的细胞迁移距离或数量。
将上述公式用LaTeX表示为：Migration Inhibition Rate (%) = \left(\frac{\text{Control Migration} - \text{Treated Migration}}{\text{Control Migration}}\right) times 100在英语中，可以这样描述：The Migration Inhibition Rate is calculated using the formula: Migration Inhibition Rate (%) = (Control Migration - Treated Migration) / Control Migration) × 100. This formula compares the migration distance or number of cells in the control group (without drug or compound treatment) with that in the treated group (with drug or compound treatment).。
YII2之migrate的使用方法
YII2之migrate的使用方法Windows10系统YII2之migrate的使用方法2018-06-14系统环境：1.系统安装的为Appserv软件，集成mysql，php，apache服务器2.安装路径为C盘的根目录下；3.选取的框架时Yii2框架的Advanced版本；备注：如果选取不同的服务器集成，只需采用cd回到根目录即可；一、进入命令提示符，进入DOS系统二、进入YII2.0的高级版本目录：Microsoft Windows [版本10.0.17134.48](c) 2018 Microsoft Corporation。
保留所有权利。
C:\Users\zengtao>cd..C:\>cd \AppServ\www\yiiADC:\AppServ\www\yiiAD>三、键入migrate命令：yii migrate Microsoft Windows [版本10.0.17134.48](c) 2018 Microsoft Corporation。
保留所有权利。
C:\Users\zengtao>cd C:\AppServ\www\yiiADC:\AppServ\www\yiiAD>yii migrateYii Migration Tool (based on Yii v2.0.15.1)Creating migration history table "migration"...Done. T otal 1 new migration to be applied:m130524_201442_initApply the above migration? (yes|no) [no]:四、选取创建、完成migrate迁移Microsoft Windows [版本10.0.17134.48](c) 2018 Microsoft Corporation。
Migrations
Iwona Sagan
19 maja 2011
RECOURSE
Research and Education Centre for Urban Socio-Economic Development
Katedra Geografii Ekonomicznej
Uniwersytet Gdański
Classification of migration according to distance
Iwona Sagan
19 maja 2011
RECOURSE
Research and Education Centre for Urban Socio-Economic Development
Katedra Geografii Ekonomicznej
Uniwersytet Gdański
Early human migrations
RECOURSE
Research and Education Centre for Urban Socio-Economic Development
Katedra Geografii Ekonomicznej
Uniwersytet Gdański
Migrations
1. 2. 3. 4. 5. 6. 7. 8. Definition of human migration History of migration Migration rates Criteria of migration types classification Push and pull factors Laws of human migration Migration movement factors Migration movement main features
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Old Commonwealth
They were in contrast with the socalled Old Commonwealth (or "White Commonwealth") countries that were located in the developed world and were predominantly white and wealion
Reasons for immigration1607-1830 Political Freedom Religious Tolerance Economic Opportunity People want a better life - better job - more money Political Refugees fear for their lives Some want free atmosphere Forced Immigration (Slavery) Family Reunification There are two types of motivation for immigration Push(need to leave in order to survive)･ Pull (attracted to new way of life)
From the early twentieth century to the 1960s, it was the chronic shortage of labour in this young developing country that attracted Italian workers. The Canadian labour market, compared to that of Italy, offered a relatively high level of employment and income. Italian immigration to Canada was also encouraged by Canadian immigration policies, which were more liberal than those of other countries due to the labour shortage, especially after the Second World War.
Urbanisation
A growth of towns and cities leading to an increasing proportion of a country´s population living there.
Counterurbanisation
villages.
Movement of people in MEDCs away from urban areas to live in smaller towns and
New Commonwealth
The term was commonly used in the 1960s and 1970s to refer to members of the Commonwealth of Nations that had joined in recent years as a result of decolonization. These countries were mostly, poor developing countries in Asia, Africa and the Caribbean with predominantly nonwhite populations.
Migration
Migration is the movement of people from one place to another
What are the main types of migration?
Migration can be permanent, temporary, voluntary or forced. It can be international or internal.
West Indies
Inner city
Violence, drugs and Police harassment muggings
Ghetto
An urban district containing a high proportion of one particular ethnic group.
Push and Pull factors
Migration can occur as result of push and pull factors. Push factors are those which force a person to move. This can include drought, famine, lack of jobs, over population and civil war. Pull factors are those which encourage a person to move. These include a chance of a better job, better education, a better standard of living.
Commonwealth of Nations, a voluntary association of 53 independent states, almost all of which are former colonies of the United Kingdom.
QuickTime?and a TIFF (Uncompressed) decompressor are needed to see this picture.
Ethnic group
The group of people a person belongs to categorised by race, nationality, language, religion or culture.
Racism
Unfair, ridiculing or threatening behaviour towards someone because of their skin and/or particular racial group.
1890-1924 ･Jews came for religious freedom ･Italians and Asians came for Work ･Russians came to escape persecution･America had jobs ･America had religious freedom ･America was hyped up in many countries as "Land of Opportunity"